It’ll probably more pricey than Toronto, and slightly difficult to figure out the “lay of the land”, ie which agencies are legit and which are bull. Theeroticreview.com is one of the better ratings sites for London. There are many other websites though, some of which seem to have BS reviews. Generally there are a lot of Eastern European agencies charging 200-300 GBP per hour that are bull, and the chick will look way worse IRL than on the site. There are also very expensive elite agencies that charge 600 GBP that are the real deal, but obviously expensive, like equivalent to 1000 CAD per hour. There are super elite model-level agencies in London for $$$, but it will probably be difficult to find something equivalent to the better-looking chicks from Cupids or Mirage for a comparable price.
With only 9 hour stop over it will be difficult, but I’d recommend getting a paid account on theeroticreview.com, then filter out for chicks with looks of 8/10 or 9/10 or better. Then be prepared to spend more than you would in Toronto, or certainly Montreal (where you can actually find hotter chicks for very little $$, like guys from New York to Montreal for hobbying).
Only one girl out of 4 I saw was a problem (kept grabbing my dick as I fucked her so I couldn't get full penetration). She was still hot though.