We are signed up for the Best of England tour which begins in Bath. After arriving in Heathrow, we will take the Heathrow Express to Paddington Station, and a Great Western Railway train from Paddington to Bath. My question is: for the GWR train reservation they require you to select a specific departure. If we don't know how long it will take to get through customs and immigration in Heathrow, how can we select an accurate train departure? Is it ok not to purchase train tickets in advance? They do recommend reservations.
I recommend just taking the bus from Heathrow to Bath.
Take the bus to Reading from Heathrow and hop on the train to Bath. You can book a specific rail time for cheaper but if you miss it you'll have to buy new tickets.
I agree with Carol
Do we need reservations for the bus?
No. Just walk up to the ticket window at Heathrow Bus Station and buy a ticket to Bath.