In the Soho walk-ups the standard charge for 30 mins is £75. In February, I had 30 mins with a Soho girl for 65 so the prices haven't gone up, per say. It's just that some WGs are trying to take advantage of naive punters who expect Brexit and other events to cause price increases.
Market forces determine the price and hence, what WGs charge comes down to what most of the punters are willing to pay.