Obviously it’ll vary enormously depending on what happens in the next two months, and potentially on where you are in the country.
Best case – if the mentalists, sorry “government”, see sense, or if you live in Norn Ireland, or if they extend the current situation, is that there won’t be any additional sales tax or duty to pay on your purchase, and it should come through as usual.
Worst case – your bike would probably get stopped by customs wherever it arrives into the UK and, given the volume of goods affected by this, would be delayed significantly. There may then be UK VAT to pay (albeit your initial price will be ex-sales tax), plus whatever duty is due on a WTO-traded bike.