So I've just spoken to M&S, the deal is £2k for existing customers (ours is a 'premium' policy so not sure if others are different), but only £1k for new customers. Importantly if you buy a bike second hand for under £2k but to replace new it would be worth over £2k you still need to specify it as it is a new for old policy. It will add a fair bit to the premium. They didn't need proof of ownership or photos etc, just make/model/any upgrades etc.