I am calculating the insurance cost of a remap.

I have 3 quotes from admiral

go get it RR'd with some asda 95RON unleaded

job done

some insurance companies will only insure you if you can supply them with an engineers report/dyno plot...

go get the plot with crappy 91 ron petrol

That should do it

If they ask you who did the tuning, and the tuner advertises gains of 40-50bhp, I think you'd be hard pushed to argue only a 10% increase

Chris