We had someone knock at our door this evening too - I’ve discovered afterwards that apparently it is a scam so please take care. I found this article via google which near on describes the activity : https://www.swlondoner.co.uk/news/25022021-knock-knock-criminal-door-callers-scam-at-large-in-south-west-london. There have been burglaries in our road in recent weeks please take care. The more we can raise awareness the better.