London is a candy store. There are all kinds of options. the hobby is legal and there are hundreds of agencies in London that can get you whatever you want. It's a business like any other. I will tell you that most agencies will charge about 300 pounds or more for an hour but the quality and abundance of ladies is staggering. Here in the US, agencies can be unreliable and even dangerous, but in London, most of the agencies are very good and there are fewer independents by comparison to the US. I recommend you look into the primary UK and European review site - Captain69
http://www.captain69.co.uk/404.php I am a member. I am going to London the first week of June. i've been there a couple of times and Captain69 is by far the best source for good, reliable reviews. You will pay, but it's worth it.
In England, hobbyists are called punters. One of the other boards to check out is PunterNet
http://www.punternet.com/forum/index.php. There is also Punterlink
http://www.punterlink.com/
These two sites will give you information on independents, agencies, and parlours and brothels. If you are only going to London, check out the whole scene. If you are going to other parts of England and Europe, there are other options to consider.
Agencies I highly recommend in London:
Allure
http://www.agencyallure.com/ run by Claudia. She will help you out. Tell her ramblinguy sent you. She is getting me set up with several of her ladies for my trip. i can verify that the photos are good
Hamiltons of London
http://www.hamiltonsescorts.com/ is highly regarded, although I have not used it myself
Blue Monday
http://www.bluemondayoflondon.co.uk/ also highly regarded by English gentlemen I trust
Bijoux Escorts
http://www.bijouxescorts.com/
These are all A+ or A rated agencies on Captain69. There are quite a few more, these just seem to be the best unless you really want to pay top dollar.
Allure and Hamiltons will have a number of English girls. Some of the other agencies will have more Eastern European ladies, but you should be able to get whatever you want with a little research.
Remember, the exchange rate is currently $1.56 per £1, so a three hour date at £300 will cost you $466, but you can almost certainly get any kind of action you want and with a really beautiful girl. keep an eye on the exchange rate. $1.56 may seem high but that is actually the best rate in many years. I was in London last May (2014) and the rate was close to $1.70, so keep track and see where it is from day to day. I recommend getting the eCurrency app for your phone or something else to keep track of the daily changes. Feel free to contact me for more advice on London. It's a great, legal place to have fun.