A bit late in the day milliesmum, but you can call the Noise Team at Wandsworth Council (assuming you're in Wworth) for noise nuisance, they usually come out to investigate and decide whether they can do anything.
http://www.wandsworth.gov.uk/a_to_z/service/232/noise
Years ago when we lived elsewhere in SW11 there was an industrial premises nearby and they had an alarm going off all night - the Noise Team came and witnessed the noise and followed up with the business to get their contact details to be able to stop it happening all night again.
Hope it's stopped by now though!