I don't know whether it's my ageing addled brain, but I seem to remember about 10 years ago I could go on AW and do a search for a 'nice but old' post code area in my local city and it would through up a reasonable number of british girls and you could be fussy about who you chose, there were very few foreign girls. I also seem to remember that I was paying between £100 to £130 per hour for an in-call. Prior to the financial massacre of 2008 money was easier to come by, at least that is my memory as I always seemed to have spare cash. Certainly my earnings have not kept pace with inflation over that period.
That £100-130 is now worth about £160-210 at 4% inflation over 10 years, so if we are still paying £100 the SPs are earning far less in terms of purchasing power than they were in 2008. I personally know one excellent English girl who I used to visit, who is now a good friend, who retired several years ago because of falling real rates. So it's not surprising that the foreign girls moved in, as with a good exchange rate, they could take good money home, at least in comparison to what they could get at home. It's basic economics.
I think we may well find that if the £ sinks further against the euro the foreign girls may go home as the farm & site workers have started to do.