[Biker Biggles]

Its a regular scam with insurers this.They wont allow chages to existing policies like change of bike,or address,or anything else without either cancelling the policy(little or no rebate),or charging a ludicrous extra amount for the change.You then lose the no claims you would have got if the policy had run for the full year,because you have to take out a brand new policy before the old one was up.
In this case I would keep your existing policy for the three months left,and buy a big hefty chain for when you leave it at work.You can usually find something solid to chain it to if you look around.Then when you renew the policy go somewhere else and tell them why you wont be back.