First post here. I have quite a bit of experience of massage/HE, mostly in west London. Generally, I've found the chinese girls tend to be an absolute dead cert whereas the Thai girls aren't necessarily. I would also agree that the better you treat them, they better they treat you...they are human after all. If you compliment them on their English (sometimes stretching the truth isn't a bad idea), tell them how attractive they are and so on, they are much more likely to offer more than a massage. Over the years I've had a range of ummm...extras including a few CiMs and even a couple of FS but that's often after multiple visits and serious chatting up. Still, all worth it.
The only problem I've found is the girls (certainly in west London) move around a lot so you can find someone you've been seeing regularly just disappears. For that reason I'd hesitate in recommending any particular establishments (and I don't want to be accused of being a pimp first post out!!) as the service can vary from shop to shop but, as a rough guide Chinese shops in the W6, W12 and W4 areas are the best bet. Prices are usually £45 for an hour massage, HE about £20/30, naked HE £40, B2B £40 plus.