When I was a lad (a little bit later than when Sarahsaurus was around), there was a common misunderstanding among schoolboys that methane was responsible for the foul smell of flatulence.  A story was told of a boy who used to set fire to his farts with a cigarette lighter, the fabric of his trousers acting as a kind of Davy safety lamp protecting his nether regions.  This was indeed evidence of methane, but methane was not the source of the smell.

However, the connection between human waste and methane did not go unnoticed.  Poo power cuts Thames electricity bill by £15m, triumphantly announced Thames Water ten months ago:

Thames Water saved £15m in electricity bills last year by generating its own renewable power from its 13.6 million customers' poo.In 2008/09 Britain's biggest water and sewerage company generated a staggering 14 per cent of its power needs from either burning sewage sludge or methane derived from it.  

And in Didcot, Oxfordshire, the famous Didcot A and B Power Stations are from this week being accompanied by a unit with a small biomethane unit: Sewage is smell of success for 200 homes, announced the Oxford Mail, with the happy prediction

If the venture is replicated across the country, sewage, manufacturing waste and farm slurry could generate 15 per cent of the UK’s gas supplies by 2020.

But how valid is this?  I myself don’t know, but I would be glad if readers could tell us of any similar projects in their own backyard.