Information and discussion on all aspects of British photographic history
OK. Well this advertisement, dated 3 April 1852, appears to offer some evidence that at least one well known London studio photographer was prepared to dip his toe in the Fox-infested waters.
In answer to your specific query about 1851-1854 I would suggest - and the evidence seems to show this - that the wet-collodion process had a slow take up after 1851. It required other experimenters to take Archer's published process and develop it further to produce a more workable process that could be used commercially. It wasn't until c1853/54 that there was a rapid rise in the number of studios once a practical process had been developed and Talbot's threat of litigation against those using collodion had disappeared. This might explain why there are relatively few wet-collodion portraits before c1854.