The fact that they are usually the other way around in Europe tells you the reason. It's not so much about which hand is usually stronger (which is the same in Europe of course), but about turning across traffic. The argument is that, when doing that, you should use the rear brake, hence left to rear in the UK.
You get some pretty zealous arguments on this, and people who can't see why anyone would do it differently. In reality, there has always been a minority, me included, who do prefer it the other way around. People talk about going over the bars from over-using the front brake, but a skilled rider shouldn't do that, and it's a bit inconsistent with modern arguments for disc brakes, which rather depend on the other types not being good enough for that risk to be real! It's important of course to remember only to brake in a straight line; front-wheel skids are much more serious, but much less likely unless you make that mistake.
I know that arguments can get zealous, and are never really resolved, because I once bought a reproduction copy of Cycling magazine from WWII days. They were arguing about it in the letters pages then, and in exactly the same terms as above.
I agree that predictability is important. If you're used to the brakes being one way around, try always to have them that way if you can. Work out what suits you, and stick to it.
