Police can only disperse people in a designated 'dispersal zone'. There's the following explanation on: http://www.direct.gov.uk/en/YoungPeople/...G_10027673

Dispersal notices
Another way that anti social behaviour is being tackled is by using dispersal orders. A chief police officer can put restrictions on certain areas that have been identified as areas where anti social behaviour is particularly high.

Once an area becomes a dispersal zone, the police and community safety officers have the power to order groups of people to leave an area after a certain time if they suspect that anti-social behaviour has or may happen, and can exclude people from the area for up to 24 hours. An officer can also ask anyone under 16 to go home after 9pm but can not force them to do so, but a refusal is an offence.

Lewisham town centre has been a dispersal zone: http://www.lewisham.gov.uk/PolicingAndPu...People.htm

But before we all rush off to ask for and SE23-wide dispersal zone, I've also found an interesting (and brief) document citing research on the limited successes of dispersal zones: https://www.policypress.org.uk/images/up..._0_175.pdf

As it says on the Directgov website, your local authority should also tackle anti-social behaviour. Lewisham's page on the topic is: http://www.lewisham.gov.uk/PolicingAndPu...Behaviour/

They say they are pioneers of a 'street warden' scheme, so why not see if you can take them up on it?

Also the Met Police's Safer Neighbourhood Teams are there to help resolve such issues:
http://www.lewisham.gov.uk/PolicingAndPu...bourhoods/

Every one of Lewisham?s 18 wards has had a safer neighbourhood team since April 2006...Their aim is to listen and talk to you, and find out what affects your daily life and feelings of security.

These might be issues such as anti-social behaviour, graffiti, noisy neighbourhoods, yobs or vandalism. Then, they work in partnership with you and other agencies to find a lasting solution.

They must be worth a try.