I had a deal with AMERICAN for my daughter and family for the same time and that was £346 via Chicago. However that deal has now closed and I think they are now charging about £50 more for the same flights.

If you check the AMERICAN web site you will find some flights that are less popular either because of time or routing which are sold at a cheaper rate.

I would have thought that the best flights for you would be the ones out of Bristol. Even if they are a bit more expensive you would more than make up for it with the cost of the trip to London and the increased cost of parking.

Regards Dave