Have you been contacted by a builder and found that you did not get a job done or to a bad standard?
This evening Wed. at 8 until 9 pm on Channel five, the work done is highlighted in Dulwich and Lewisham, they have moved on but are they now near you?
Even if you have not been involved, you might see these persons offering to do work. You could warn a neighbour if they are at their house. If you think that they are suspicious write down the number of their vehicles, as they wont display who they are on the plain vans.
If the van is hired to them, it might be traced.