Here's my situation.

I'm flying LHR to ARN with BA in Economy. Once at ARN I'm connected onto a Qatar flight in Business to DOH and on to HND. Both flights are ticketed separately.

Since both are OneWorld airlines and I'm flying from one to get the other am I allowed to use the lounge at Heathrow T5. I can't quite recall if I am or not, I remember reading something that said those on connecting flights with lounge access are allowed to. I've also got a Star Alliance, Virgin and SkyTeam Gold but am just a Bronze with BA so know that's no use in T5.

Thanks in advance.