On 18 June, 17:37, Jon wrote:
Possibly a disusued sewer vent. These were installed in various places
to allow excess gas to escape from sewers and tended to be tall so the
gas would disperse without creating a stink or a fire risk.

Good answer. Looking at this map http://www.sewerhistory.org/images/b...930_bmm315.jpg
that the South London High Level Extension sewer runs nearby

Thanks

Rob