From Inktober posts Oct 2018 part of the Pick and Choose History of Courtenay Street, Kennington and Lambeth:

Prince of the Welsh? Well the Prince of Wales has owned most of Lambeth for a long time, but it seems more likely that the Welsh were attracted here in the 18th and 19th centuries because of all the market and private gardens. So many came that Allen in his history of Lambeth (written in 1827) says that the hiring fair by St Mary’s became known as ‘Taffy’s Fair’. I also found out that young women and girls would set off from Tregaron in Wales at one minute past midnight on a Sunday (to avoid working on the Sabbath) to begin the long walk to London where many of them worked in market and private gardens. Some picked strawberries and sold them in little baskets at roadsides, others worked weeding in gardens and some worked in the dairy trade. Looking at a trade directory from the early 1900s I had already noticed how many of the dairies and milkmen had Welsh surnames, and it seems their involvement in the milk trade has deep roots.