Or is that due to fluctuations in the exchange rate? As you are buying direct from a shop on the continent I expect that the UK price will be effected on a day to day basis. Apparently (I didn’t know as I don’t have to deal with exchange rates anymore) a couple of weeks ago it got down to 1.1 eu/£1 for a few days.
If you are dealing with a company such as Trek for instance, they will have agreed an exchange rate for their UK distributor/agent. This will mean stable prices to a degree for the UK market. However a prolonged variation may well mean a price change when a new batch of bikes are imported I assume. I’m assuming the UK distributor will have a few hundred (or even tens maybe of very high end) in stock, which is why a popular bike will sometimes sell out.