I spoke to the Forest Hill police yesterday about this issue and was provided with the following information:

If you want to see something done about this I would urge forum members to report such incidents (however trivial) via 101 so that the police can build up a picture of where and when these incidents are taking place, so that they can be on the scene at future occurrences.

In other information from the Forest Hill police panel, the reported crime statistics in Forest Hill ward (and Perry Vale) are really quite low over the last few months. Of course every crime is one too many, but the numbers of burglaries and drugs offences are significantly lower than previous years. A lots of this is almost certainly down to the police catching and prosecuting a few individuals, who can each create their own little crime waves.
you can view recent crime statistics for Forest Hill at http://www.police.uk/metropolitan/00AZGL/crime/
for Perry Vale at http://www.police.uk/metropolitan/00AZGS/crime/
and for Crofton Park at http://www.police.uk/metropolitan/00AZGH/crime/
One thing that is clear from the statistics is that anti-social behaviour is the main type of crime reported, so please don't feel that aggressive begging or street drinking are not worth reporting.

The police do read SE23.com, but they cannot act on reports via the forum from anonymous posters. As well as reporting incidents by phoning 101, you can email the police at:
ForestHill.snt@met.police.uk
PerryVale.snt@met.police.uk
CroftonPark.snt@met.police.uk