Michelle Bentham of the British Geological Survey said the team constantly monitored and measured soil and atmospheric gas and found high levels of gas in different places at different times.

He confirmed there were high levels of methane gas in the area, but said those levels had decreased since the borehole filling work, a “good indication that it’s working”.

John Finley of the Ground Source Heat Pump Association (GSHPA) said: “This is the only known shallow gas formation in GSHP operations in the UK for over 25 years.”

He said it was a “tragic incident” that was being taken seriously.

“We will make changes where necessary, changing standards and procedures that are currently in use,” he said.