The Mysterious Wimbledon 'Flue'

Before I continue with the results of a recent trip down the Kings Road, I thought I'd throw this enigmatic object into the mix. I really don't have much of a clue as to what it might be, but it does have an air of mystery about it as well as a clue or two.

Spot the 'flue'. Tucked away and very inconspicuous

As you can see from the photo above it's not very big, nor very prominent. Roughly A4 sized and up against a wall I think it was the markings on it that actually caught my eye more than anything else. 

A hollow metal flue. Could it have been for cables?

This view shows, I hope, the fact that it seems to be a hollow pipe - and the only reason I can think it might need to be hollow is that it was either for ventilation or for cabling. Obviously the main marking is the arrow sign, which crops up quite often on pavements, walls and other places.  It's the symbol used by the MOD or the War Office I suppose, in its early days, is called a Broad Arrow or a Pheon.  Interestingly it was also used to mark prisoners outfits at one point which was the origin of all those Beano-esque cartoons of villains in arrowed uniforms. The other common use that seems to pop up quite regularly is when it  is used by the Ordnance Survey to mark measurement points around the country but even here the word 'Ordnance' betrays a military origin to its usage..

It's a crisp and un-weathered casting with what looks like the MOD insignia.

The question is what was it for? The first picture shows a suggestive tarmac outline around it, possibly (or possibly not) indicating some sort of subterranean floor plan. Was it for air? It looks very narrow but maybe there's some sort of bunker underneath (presumably Wimbledon Common would have been seen as a possible glider/paratroop dropping area)? Maybe there's no bunker but an old military communications point of some sort. Or maybe it's neither and instead it's a hollow survey mark with the groove on the rim indicating the measuring point.

Bit of a mystery then, but any suggestions gratefully received!

(In response to one of the comments posted, the site is almost opposite the  drinking fountain by Cannizaro Road (B281)  and in front of a very nice house. However I do like the suggestion of a Womble letter box!)

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