Contact your SNT (police). An old friend of mine (now deceased) was a 'victim' of a door to door scam some years ago. He mentioned it to our local SNT police officers who found that several ED residents had been visited by these ;salespeople. It was arranged that my friend asked the scammers to return on a certain day and time when he had some money to purchase their goods. Police in plain clothes outside in street watching. with a uniformed officer in the house - scammers returned and were arrested.
The East Dulwich Community Centre in Darrell Road have 2 halls available for hire. They may have some spaces free. Check their website for pictures and email address.