Thanks everyone for the input,
As it turns out I can get about 80% of the premium back if I change, I will also lose any no claims earned as part of this policy.
Insurer charges an additional sum (35% approx) on the original policy, not just for the increase in engine size but also for the privilage of changing the car insured.
For instance the insurance would be 25% cheaper if I had insured the new car first time around with them rather than changing to it mid stream