Originally Posted by
guv1976
Why does it have to be priced in GBP?
If you have a GBP-denominated credit card and you charge the flight to that card, the USD ticket cost will be converted to GBP anyway.
Yes, but for a fee of typically 1 to 3%, unless you have a card like the Post Office Mastercard (actually Bank of Ireland).
However if you ring up the BA Service Centre, they can charge you in GBP. If you're paying with BA Amex PP that is worth doing since they are a 3% fee charger.....
Single trips (is it really single? Can you think of some other trip to connect this in to?) are one of the few reasons for using Avios, since there is good availability in WT and WTP, it's flexible-ish to 24 hours, and isn't cost loaded for being single. It may even be worth buying Avios directly or via charge card deals, Tescos etc.
However I would suggest you look at US Airways from PHL to London, Edinburgh, Manchester, Glasgow, Dublin, Shannon: the cost could be lower (haven't looked), and PHL is surprisingly well connected to the Washington area by train.