Oh Dear! It appears that the leak did come from Sunderland Depot, and here are peoples comments below:

"It was confirmed it was at the stagecoach bus depot 1 of the cylinders had burst open hence the noise and smell of gas"

"Gas leak was at the depot for the busses"

"It's the busways depot, I live in Howick park"

"Its the gas tanks at the bus depot happened about half three really loud hissing noise could here it at Tesco"