Actually the Airmiles coversion is 250 points (250GBP) spend to 40 airmiles or 80 if you spend the required 60GBP a week on food/drink at Tesco.. this was/is on their website.

If BA Miles are moving as well then it should be 10:1 ie 400/800 BA Miles.

This is what I had hoped for as we spend 100GBP a week at Sainsbury/Tesco so roughly will be looking to 'earn' 1500 BA Miles a month ... 18,000 a year on top of flights/Amex spend plus the 150 BA Miles already earnt on Amex on the 100 spend .. plus the WT+ and 2 for 1 offer with Amex = close to 2 WT+ trips to the US a year.