I can honestly say that I have never actually been caught out during a raid, but they do happen. The recent trial involving the 'Libra Club' in Birmingham is an example of what can happen, likewise 'Cuddles', as mentioned before on the Hagley Road. I'm afraid the scene has changed since I first started using them back in 1980, when the girls were English, often local and doing it to make ends meet, and perhaps enjoy the work too...if you landed lucky!
I drive down the Pershore Road daily, passing two Parlours, Kitty & Co and At Your Service. On one occasion I did see a Police Van outside At Your Service. It's often related to trafficking I'm afraid, EU and/or Asian girls forced and coerced into some establishments. A recent punt at Kitty & Co was awful, a Romanian girl who was so unresponsive, and clearly in a bad situation. I had a similar experience at At Your Service. Both are relatively cheap, so with a great deal of things you get what you pay for I think. On the other hand, the best experience I had was at Manyana in Selly Oak, it was with Kellie, a little petite cracker from Wolverhampton, so she had the Black Country Accent and was very responsive, and seemed to enjoy her 'work'. It's a risk, part of the thrill for me is the unknown, and the anticipation of possibly finding a punt that is rewarding for both parties. Good luck with your research, do follow up with any reports and reviews.