Originally Posted by cammyloon

I think the thing to do is simply treat the car hire as a separate booking - don't try to link to your 2-4-1. You can still book via www.avisba.com. Or simply shop around for the best deal - and you can always use your saving to buy extra avios.

Chances are you'll have to pay a considerable mark-up (and get a reduced choice of vehicle) if you simply walk up to a counter.