Bitterness over the British Gas engineers’ dispute was revealed on Tuesday when MPs heard details of distressing incidents since the row over pay and conditions flared.

Members of the GMB have staged 12 strikes this year and will walk out again on Friday for four days, as the union campaigns against new contracts it says cut pay and increase the working week for engineers under a so-called fire and rehire policy.

Chris O’Shea, chief executive of British Gas owner Centrica, told the Business Select Committee that his wife and teenage son had received a package of excrement, while police have been involved in helping some staff travel home.

In his evidence, GMB national officer Justin Bowden said that, in his 25 years as a union official, he has never seen so much pressure put on workers to accept new contracts, including an “endless stream” of emails and telephone calls.

He told MPs that the GMB has a history of successfully agreeing changes with companies, including British Gas, but he criticised the threat of fire and rehire.

He accused the company of “poisoning the well” by issuing formal notification of changes to contracts last summer before an agreement could be reached.

Engineers are being told to work “harder and faster”, with a longer working week, he said.

Mr O’Shea said his aim is to protect well-paid jobs and improve the competitiveness of the company rather than see a continuation of redundancies and a move to employing more contractors.

Basic pay rates are being protected and it is “reasonable” to increase the working week by three hours to 40, he said.

Mr O’Shea called for a clarification of the law on issuing formal notices about changes to terms and conditions, adding that he is committed to working with the GMB to try to resolve the dispute.

Concerns have been raised that some employers are resorting to tactics such as ‘fire and rehire’ and seeking to downgrade pay and workers’ terms during the pandemic

Committee chairman Darren Jones, Labour MP for Bristol North West, said: “Businesses and workers have had a very tough time over the last year.

“Over 800,000 people have lost their jobs since the pandemic took hold and there are very real fears that many more people will face the same bleak fate over the coming months.

“There is no doubt that many businesses have faced difficult trading conditions, but concerns have been raised that some employers are resorting to tactics such as ‘fire and rehire’ and seeking to downgrade pay and workers’ terms during the pandemic.”