When you consider that the "natural gas" we get from places like the north sea and other places is virtually the same stuff, then this is a very viable concept indeed.
It looks like we could become more and more reliant on importing gas from abroad in the future with the effect of banging up the prices considerably - which has already happened with the suppliers blaming the wholesale price increase.
It would be prudent for this scheme to be taken up seriously across the whole of the country, as this would help to stabilise costs and (if/when) we reach a point where supplies of the natural stuff are in danger of becoming depleted - at least a mechanism would be in place to continue supplies - by then, the system (hopefully) would have matured and improved to the point where gas yeilds from sewage treatment would be substantial enough to continue supplies - possibly permanently. In any respect, it would also possibly protect us from being held to ransom by greedy and unscrupulous wholesale gas suppliers - like (on the news some time ago) with Russia and Europe.
Suppose really this concept is not too unlike an undertaker's business (no offence), I.e. as we all are destined to eventually die, similarly all of us have to poo, so (in essence) there will always be a ready supply of the raw materials to keep the system going.
Better to keep these particular eggs in several baskets don't you think.
Si thee