I'm not convinced about the benefits of doing this, and I suggest you do the maths carefully for the particular bike you are interested in.
I plan to buy a bike at the start of next year and have been doing the research. And at the moment my plan is to buy it in France and import it into Switzerland. There are other forum threads on the details of doing this, but essentially it's similar to the details above - you get the France (rather than UK) VAT back and have to pay the Swiss VAT to bring it back into CH (or not - I already did this for a cheaper bike and the Swiss customs guy couldn't be bothered to do the paperwork, so didn't charge me at all).
And the benefits of importing it from France are: 1. You buy in person from a French cycle shop just over the border, so you know exactly what you are getting, 2. You don't have any shipping or other charges, 3. The process is simpler than doing the UK thing (I would argue).
(Oh and the brakes are the "continental way around!!)
I guess it's all down to the price comparison, but for what I'm looking at, the prices are no cheaper in UK than in France - so I think the France option is the cheapest and least hassle option. If on the other hand you get a good price / discount from a UK store then it may be worth it.
Comments from others? (And sorry if you thought this thread was finished!)
Stuart