SD - this is what I would do even though I DON'T shop at Tescos on principle.
Go into Tescos 10.30am on any one of the saturdays leading up to Christmas when it is really really busy. Make sure the store manager is in. Do your main shop, loads of stuff, tons of it, get to the point of paying, make some excuse like you've lost your wallet/it's been stolen, go looking for it, some how get the store manager involved, they will want to help and for you to find it asap as otherwise they will have lots and lots of angry customers at the check out who are being held up by you, you're not sure where it is so take him out to the bike racks where your bike is parked, in passing mention the totally inadequate crap siting of them and see if he agrees and is sympathetic to getting them moved away from the wall. Then miraculously your wallet turns up say in a secret pocket or from deep inside your panniers, you apologise profusely, pay whilst still apologising to all around you and quickly reminding the manager of the bike racks, off you go, mission accomplished

. Nothing to lose ........