A cheaper way may be to have flying excluded from your "normal" life insurance and buy a separate Personal Accident purely for flying.
I made a vague enquiry a short while ago, and I think I could get up to 4x salary as a death benefit for a premium of 100-150 per year. This would have been with a Lloyd's Syndicate via a broker.
I would imagine any aviation insurance broker advertising in the the UK magazines would be able to advise you on likely costs.