I don't think BA have a RTW award. The most open option is a mileage-based award whereby you add up the flight distances and that generates the mileage required. But these tend to be very expensive.
You are better off breaking the journey into a few oneway legs which involve only one partner, or BA + 1 partner airline. These price up more conventionally, based on start and end region.
This page will give you the numbers.
http://www.britishairways.com/travel...g/public/en_gb
If you list where you want to go you might get some good advice.