Insurance Conundrum

Hey all I will try to explain this as simply and as quickly as I can.

3rd party, fire and theft will cost me around £250 for the premium and about £1100 in total for the excess.

3rd party only will cost me £400 for the premium with no excess.

If I make the assumption that I won't claim, it's cheaper to get 3rd party, fire and theft and a good chain and lock.

Under the assumption that I am going to claim it's far cheaper going for third party only.

My thoughts are I should get 3rd F&T, a good chain and lock and make sure I don't do anything that causes a third party to claim against me. By the way the bike will be keep in a locked garage and we have a dog!

Anyone with differing opinions?