If this happens to you hang around nearby or by the bike and get a good  face photograph of person unlocking the bike chained to your one,and give to the police.May already be known to them and if they get a few pictures of him may watch or follow him.

This happened to my husband outside the Southside Shopping Centre.He cotton on straight away to what was happening so he asked the security guard to cut the lock.

Details received from another local social media platform:

Just want to warn everyone about something that happened to me this morning in Balham. I locked my bike up on Hildreth Street to attend a fitness class nearby, once I came back around 50 minutes later my bike had been locked and secured to a very tired looking bike.

This was no ‘accident’ as it had been secured to the tiny section at the back near the chain. Apparently this is now a new way to steal bikes - they wait for you to give up and leave it and then break into your lock at night. Luckily I waited with my bike and called 101 to report the incident to the police (although there’s not much they can do) but the culprit returned 30 mins later to unlock the bike behind my back once they saw I wasn’t giving up.