Thanks for the warning

No need to jump straight back on train home, plenty of girls to try around Stratford/Leyton and a 2 mile radius. All plenty closer to Essex and some worth having a sniff at. Given the state of the London market if you're trying to punt for less than 150 then there seem to be a lot of displaced girls circulating past the Zone 4 boundary and into the adjacent counties e.g. The pretty Latina crew with their own websites have a place Barking way as well as their sites nearer Canary Wharf.
Do the research, unless there are very specific destination girls with great rep in the centre, worth saving time and money dipping the assortment closer to home (but not too close). Good luck.
Re: specifically black Brit escorts, the odds seem to be against us in finding even passable providers below 200ph. Reading reviews and doing background on searches these last couple of years has surface a scant few that get some mention of worth here. Slightly better odds with the mixed race Latinas provided you don't want more than vanilla without riding the extras train.