Not particularly.
AA does have main cabin extra on many aircraft which provides extra legroom although with economy service. Perhaps look at ex-EU CW fares.
Nux thanks for the answers. I suppose just wanted to know whether I could use avios to upgrade at any stage after purchasing the ticket whether via BA or AA. The answer appears to be no so I'll just hope for a cash upgrade on the return. I have a limited amount of time to travel so don't have the time to waste with positioning flights so ex-EU isn't a viable option even if it would only be a couple of hundred more. Plus I'm young enough to not suffer if I'm in an economy seat but I am catching a night flight back to the UK and heading straight to work so that's why a bit more comfort would be appreciated on that leg.
I had thought you could use avios if there was milesaaver availability but from your answer I think that's wrong.
When I mentioned the exit row it's because I assumed that if the second flight was operated by BA I could reserve it as a gold even if on a AA ticket but correct me if I'm wrong.
Thanks for the help.