The safety of the pressure vessel “heart” of the Sizewell B reactor has been thoroughly assessed in the light of cracks found in two Belgian nuclear plants, a government minister has assured MPs.

Replying to a Parliamentary question, Michael Fallon, Energy Minister, said that the Office for Nuclear Regulation (ONR), the UK nuclear safety watchdog, had reviewed records of the manufacture of the steel vessel and other documents supporting its safety.

“ONR judge that the validity of the reactor pressure vessel safety case for Sizewell B is not affected by the recent observation of flaws at Doel 3 and Tihange 2 in Belgium,” Mr Fallon said.

The written question was submitted by Paul Flynn, MP for Newport West, at the request of Charles Barnett, who lives in Dunwich and is chairman of the Shut Down Sizewell campaign.

Mr Flynn asked the secretary of state for the environment, Owen Paterson, what Sizewell B safety reports he had received from the ONR following the “serious flaws” found in the Belgian reactors.

Mr Barnett had approached the veteran Labour MP after expressing dissatisfaction with the response to a similar request in a letter to his own MP, Conservative, Therese Coffey.

Dr Coffey decided to refer Mr Barnett’s letter to John Jenkins, chief executive of the ONR, saying: “I use my judgement on who will offer the most useful answer for my constituents.” But Mr Barnett, who had already received assurances over Sizewell B safety from the ONR, maintained the issue should be raised in Parliament.

Mr Barnett said yesterday that Mr Fallon’s reply was “quite unacceptable” and that the Shut Down Sizewell campaign would continue pressing for the next in-service inspection of the Sizewell B pressure vessel – scheduled for the spring of 2016 – to be brought forward as a matter of urgency.

The ONR says there is no justification for bringing the date forward. The last in-service inspection of the Sizewell B vessel was carried out in 2005 and no defects were found.