The origins of the surname Quelch are inadequately explained by the entries found in various surname dictionaries. 
    Original research by the author has determined that the surname is mainly found in south-east England with its focal point in the county of Berkshire. By counting all of the Quelch entries recorded in the various British telephone directories for the year 1980 and organising these entries into county-like groupings, Berkshire was found to have the largest number of entries (50). The Berkshire directories included 2.5 times as many Quelch entries as did the Oxfordshire directories which had the next highest number of entries for a single county (19), and more than 1.5 times as many entries as found in the London/Middlesex/Hertfordshire area (32), the entries for which were difficult to separate into individual counties. Considering that Berkshire is a very small county, a ratio of the number of Quelch entries for every hundred thousand people was determined and indicated that the surname Quelch occurred 19 times in every 100,000 people in Berkshire as compared with 8 per 100,000 in Oxfordshire and 4 per 100,000 in the London/Middlesex/Hertfordshire area. This suggests that the origins of the surname Quelch probably lie in the Berkshire area.
    The number of entries included in the International Genealogical Index (IGI) supports this theory. The IGI is an index recording extracts of millions of baptisms and marriages which occurred between the 1500s and 1800s. When the entries for each county of the UK are examined, the only counties to include a considerable number of entries are the three listed above: Berkshire (441), Oxfordshire (81) and London/Middlesex (134). However when the entries included the IGI are divided into the centuries in which they occurred a different picture emerges as follows:

     County                        1500s              1600s           1700s         1800s

     Berkshire                        5                    58                  297             81

     Oxfordshire                    27                   45                    7               2

     London/Middlesex            0                    38                  22             74

These figures suggest that Oxfordshire could have been the county of origin of the surname Quelch. They also suggest that the surname died out in Oxfordshire late in the 1600s while increasing in Berkshire during the same period. As no other county included any Quelch entries for the 1500s, with six nearby counties including between one and five entries for the 1600s, it seems likely that those with the surname in London and the other nearby counties probably emigrated from the Oxfordshire/Berkshire area.
    Clearly the information so far discovered suggests that the surname was originally peculiar to the Oxfordshire/Berkshire area. Yet this is not reflected in the surname dictionaries which attempt to record the origin and derivation of the surname. 
    All of the surname dictionaries agree that Quelch is locational in origin, that the progenitor of the surname was "a Welsh(man)". However they differ in their analyses of the derivation of the surname. Bardsley in A Dictionary of English and Welsh Surnames compares the derivation of quelch from welsh with Gwyllam for William, Quilliams for Williams and Quhitelaw, Quhitehead for Whitelaw, Whitehead. He quotes a few examples from London parish registers such as Quilche (1612), Quelch (1613, 1655) and in particular notes the different spellings in the references to the same person Margaret Gwelch and Margaret Quelch (1686 and 1688 St James Clerkenwell) as evidence of this theory. He also adds the following ratio "London 3; Oxford 8" indicating that he was aware of the greater frequency of the surname in Oxfordshire. Ewen in History of Surnames of the British Isles uses the same example of Margaret Gwelch/Quelch in referring to the derivation of the surname under the heading "evolution by variation and corruption". Harrison however in Surnames of the United Kingdom suggests that Quelch is Celtic and Teutonic for Mac Welch meaning "son of the Welshman" while Weekly in The Romance of Names states that Quelch represents the Welsh pronunciation of welsh.
    If quelch did mean welsh it would seem logical that a reference would be found to quelch in a word dictionary as an example of a sound or spelling change over the centuries. However although the entry for welsh in the Oxford English Dictionary lists many spellings of the word over the centuries none of these include quelch. This suggests that quelch was probably an unusual and less well-known form and as such was unlikely to have been the welsh pronunciation as this surely would have been recorded. Furthermore the Encyclopaedia Britannica records that Wales is known as Cymru, Gwalia or Cambria. From Gwalia could come gwelsh and hence quelch however if this was the case pockets of the surname could have occurred anywhere Welsh people settled. As the surname appears to have been peculiar to the Oxfordshire/Berkshire area the evidence does not support Weekly's theory.
    The history of the letter "Q" in the Oxford English Dictionary explains that the sound now spelt as qu- was recorded in Old English as cw-. After the Norman Conquest qu- gradually replaced cw-, being used for all instances of the sound by the end of the 13th century. Harrison uses this knowledge to produce his derivation of Quelch. He suggests that it was Celtic and Teutonic in origin and comes from MacWelch, the ma- being dropped and the internal cw- becoming qu-. This would seem logical except for the fact that mac is the Irish, Gaelic and Manx word for "son" and no references to the surnames MacWelch or Quelch have been found in Scottish or Irish records or indexes such as the IGI. Furthermore as Welshmen must have settled all over the UK, as reflected in the fact that Welch/Welsh are relatively common surnames, this does not explain why the surname Quelch has only been found in Oxfordshire prior to the 1600s.
    Bardsley suggests that Quelch derives from Welsh in the same way that Gwyllam and Quilliam derive from William. However Cottle in A Penguin Dictionary of Surnames states that Quilliam is the Manx Gaelic form of the son of William, the "Q" being the remains of Mac and his theory is supported by the fact that both Quilliam and MacWilliam are found in Scotland.  Gwyllam on the other hand is the Welsh name for William. Bardsley and Ewen's examples of Margaret Gwelch/Quelch are used to support their similar theories concerning the derivation of Quelch however as this is the only occurrence of Quelch being recorded as Gwelch that has been located by the author it seems more likely that this is a case of an inaccurate recording of the surname; as g- is the voiced version of k- (the initial sound of Quelch) the surname would sound like Gwelch if spoken by someone with a head cold or "adenoids".[1] 
    Bardsley also compares Quelch as a form of Welsh with Quhitelaw and Quhitehead for Whitelaw and Whitehead however as the latter commenced with the sound represented in Middle English as wh- (OE hw-) this has a different derivation to w-.  Interestingly, the history of "Q" in the Oxford English Dictionary indicates that in certain dialects of Middle English, particularly in Scotland and northern England, qu- (spelt as quu-, qv-, qw-, quh-, etc.), was not confined to replacing cw- but was often used to replace ME wh-.  The root sound wh- leading to the spelling variation quh- therefore has a different derivation. 
    Although all of these theories are historically accurate in their ability to account for the derivation of various sounds and spellings, none adequately account for the fact that the surname Quelch was apparently peculiar to the Oxfordshire/Berkshire area prior to the 1600s. If these theories had been correct the surname should appear elsewhere and in other forms. As it does not appear elsewhere or in other forms the question must be raised as to whether the surname was peculiar to the Oxfordshire/Berkshire area because it was dialectal in origin.
    Significantly, evidence has been found to show that a word quelch was part of the Berkshire dialect prior to the 1900s. Wright's English Dialect Dictionary published in 1903 records that quelch was a verb found in the Berkshire dialect meaning:

     a) to swallow;

     b) Of horses; to make a peculiar noise internally when trotting.

     As such, it is possible that the surname developed from one of these dialectal words as a nickname.
    Of greater significance, however, is the fact that a 20th century Berkshire document has been found in which the word quelsh was used to describe a Welshman. The Pangbourne marriage register, which was transcribed earlier in the century, contained the marriage of a man whose name was recorded as "Jeffrey ap Richarde". The word ap is Welsh for "son of", Welsh people having used their father's given name instead of a surname until recently. Against this entry the transcriber wrote:  "Evidently the Quelsh? - ap Richard". Clearly the transcriber was attempting to convey to researchers that "ap Richard" signified that the person was "evidently" Welsh. As the transcriber was attempting to impart information, he or she would not have used a word that nobody understood. This indicates that the the word quelsh was in use in Berkshire as a way of referring to Welsh people as late as the early part of this century. Yet the word is not listed in any major dictionaries. As such, this suggests that Quelch/Quelsh was a Berkshire/Oxfordshire dialectal word describing a welshman and probably accounts for the fact that the surname was originally peculiar to the Berkshire/Oxfordshire area.
    Researcher George Bayliss of Canada has another possible theory. A home of a large Quelch family in the late 1500s was in Benson/Bensington parish in Oxfordshire which lay on the Berkshire border near Wallingford. George raises the possibility that Quelch was a corruption of Colche, a Colche family being recorded in Feet of Fines (land transactions) for Bensyngton in 1427. However this does not account for the fact that the word quelsh apparently had a specific meaning in the Berkshire dialect.

[1]  The author has found that her own surname Baxter was written down as Bagster when her speech was influenced by a headcold/laryngytus.