Self: Your logic was impeccable; buy a replacement padlock for the motorbike lock/chain & it turned up very quickly.
However, did it not dawn on you that you had to buy a new lock as the old one was locked shut around the chain ends & you can't find the keys? No, it didn't, did it!
So, you now have a nice, shiny & very expensive padlock sitting useless!
Makes mental note to dig out angle grinder tomorrow to try to remove the old one (& set the garage on fire in the process!)