Brian Gaff presented the following explanation :
Both gas and water have extensive contracts going on replacing the now very
old pipes, in the case of gas because they are obviously steel and rusting
away, and in the case of water mainly due to them being made of lead, which
although probably safe after all this time does deteriorate of course.

Our old system had 70 year old steel pipes running along the back
gardens. Leading up to their replacement 3 years ago, they regularly
came along with a sniffer in case of serious leaks.

3 years ago, they laid a new plastic main at the front, along the road,
then up drives to the individual meters. There were too many garages
and extensions built over the original pipe route at the rear.