British schools in Hongkong

Yes. There are and they vary depending on whether you are interested in IB or the A-Level system as well as how much you can afford to pay.

That article Maximillien posted is somewhat out of date. As of next year the ESF system will no longer be subsidised and therefore may end up being in the same price range as other international schools. The prices listed also seem to be out of date so certainly check with the schools you are interested for the correct price range.

If you are after rigid British system schools look at Harrow, GSIS (German-Swiss) and Kellett. However there are many British students who do exceptionally well in ESF and other international schools as well. I know many British expats who send their children to the French International School for example.

Your two biggest concerns will be placement and expense. Places can be hard to come by in International and ESF schools and you may end up on a waiting list so look to more than one school. Some schools offer ways to pay a debenture or related non-refundable fee to gain access to limited "paid" places.
ESF schools are zoned based on the area you will be living, so that may also be something you need to take into consideration.

Hope this helps. My children are in the ESF system and I am very happy with their education.