35 is the limit for issue of the Class One medical using the standard exam, although the good news is that I believe you can still get a class one issued if your BMI is above this with some further testing. As you say this may involve more rigorous cardio testing like a stress test, a mechanical evaluation etc. I also had a mate who was issued with his Class 1 medical but with a restriction of 6 monthly medicals until his weight was reduced to a level acceptable to the CAA. Basically the CAA will normally work with you to get a medical issued, once you have the initial class one issued then the 35 bmi is no longer a restriction for renewal. My advice would be do all you can to get yourself under the 35 for the initial atleast and if you are concerned then call the CAA medical department, I have always found them very open to these sorts of enquiries.
Cheers