Use the search
If you use the search link at the top of the page and search the topic of "London" for the last few years you will find that the subject gets discussed from time to time.
The short answer to your question is that the house edge is quite substantial. I've only played in a couple of London casinos and both were too small to wong. They do allow back betting, though, but you have to find someone who knows how to play to use that strategy.
Good luck.