Davep,
I too had a "problem" with my BMI and the Docs at Gatport Airwick basically said I had until my renewal to lose two points (Mine was mid thirties).
The way to calculate your BMI is:
KG. .-----. .Hieght in Metres (squared)
Any thing over 30 for a male is obese (29 for the women)
Hope this helps.
TBL