The not-so-potty idea is the brainchild of the Bath Bus Company, and it’s just the jobby for lucky passengers who will be transported along the A4 between Bath and Bristol Airport using state-of-the-fart technology.

The 40-seater ‘Bio-Bus’ runs on biomethane gas generated through the treatment of sewage and food waste. The brightly coloured bus can travel up to 186 miles on one tank of gas — equivalent to the annual waste produced by five people. On that basis the annual waste generated by one bus-load of passengers could fuel a return journey from Land’s End to John O’Groats.

The gas is generated at Bristol sewage treatment works, run by GENeco, a subsidiary of Wessex Water. And they’re not just going through the motions – the fuel produces fewer emissions than traditional diesel engines and is both renewable and sustainable.

Mohammed Saddiq, GENeco general manager, said: “Gas-powered vehicles have an important role to play in improving air quality in UK cities, but the Bio-Bus goes further than that and is actually powered by people living in the local area, including quite possibly those on the bus itself.”

Bristol sewage treatment works processes around 75m cubic metres of sewage waste and 35,000 tonnes of food waste every year. A total of 17m cubic metres of biomethane – enough to power 8300 homes – is generated at the plant annually through the process of ‘anaerobic digestion’.

Charlotte Morton, chief executive of the Anaerobic Digestion and Bioresources Association, said: “A home-generated green gas, biomethane is capable of replacing around 10 per cent of the UK’s domestic gas needs and is currently the only renewable fuel available for HGVs. The bus also clearly shows that human poo and our waste food are valuable resources.”

Up to 10,000 passengers a month are expected to travel on the ‘number two’ A4 bus service. We still wouldn’t want to be in the vicinity if the poop-decker backfires – but it just goes to prove that where there’s muck there’s gas.