If you are going significantly over £1000 - then I would have a good look at the UK first, and try and compare brands. My father often spends £5000 on a bike, and he swears the UK is cheaper. Sub £1000, I wouldn't bother, as you could get a sale in either country that would offset any advantage.
You also need to consider warranty etc - but I would have thought they would be international.
Not sure if Bike Force is national - but they are big in WA and look very similar to Evans Cycles.
Saying that - there are some good websites that offer very cheap stuff from Asia - but it may be counterfeit - so be careful.