My own 2c worth, trying this the other way, EDI-LHR, a few times over the years is that with 1 car/hotel night is that you can't always get a deposit including if it doesn't meet certain criteria (as in a minimum number of nights inc a Saturday night stay)

Probably worth a call to BAH and see what they say?

It's also published in their Ts and C's

5.1. When you make a booking we will either ask you to pay the price in full, or, if your booking meets certain criteria, we may offer you the option to pay a deposit.

6.16. Some bookings must include a minimum stay of 3 nights including a Saturday night to qualify for certain prices advertised by us. (probably more for flight + hotel bookings)

https://www.britishairways.com/conte...and-conditions