That is a fine plan - I was also thinking that perhaps a few days/weeks of emptying the tank at night and refuelling in the morning might cause them to give up their handy little filling stop.

Are there any other deterrents on the market? Obviously in the 70s locking caps were introduced, but now the scale of the problem I'm presuming will be reduced as it will only be scooters/bikes with easy access, perhaps manufacurers won't come up with anything.

Has anyone got a bike cover, and does this deter the opportunists?

Oh, and the police advice - keep the scooter in the garage. D'oh! now if we had a garage.....