A decision to exclude a watchdog group from a meeting about the Sizewell emergency plan is helping to destroy public confidence in the independence of the Office for Nuclear Regulation (ONR), according to the group’s chairperson.

Marianne Fellowes, chair of the Sizewell Stakeholder Group (SSG), said she was very disappointed that the ONR had refused to allow an observer to attend the meeting – about the future extent of the area around the nuclear site for which detailed emergency plans should be formulated.

The existing zone extends to 2.4kilometres and excludes most of the built-up area of Leiston.

The ONR meeting was attended by officials from EDF Energy, owner of Sizewell B, and Magnox Electric, in charge of decommissioning work at Sizewell A, as well as a delegate from Suffolk County Council.

Both EDF and Magnox believe the existing zone is adequate for the risk involved.

However, the SSG and a significant number of people who responded to a county council consultation believe the radius should be extended to at least 4km – in line with international guidelines following the Fukushima nuclear accident in Japan.

Local anti-nuclear groups are pointing to the evacuation which took place in Japan and are calling for the radius to be at least 20km.

Ms Fellowes said the ONR decision-making process was very important to SSG members who had devoted time and energy to take part in the public consultation. But the group had been told that it was “not appropriate” to send an observer.

“I am disappointed as it would have been very easy to exclude the public from other items on the agenda. Decisions like this destroy the public confidence in the independence of the ONR,” she said.

Ms Fellowes said she had requested a copy of notes from the meeting.

An ONR spokesman said the meeting had involved organisations with legal responsibilities relating to the emergency plan.

“Although we won’t be publishing notes of this meeting, ONR will publish our project assessment report which will explain the basis of our decision on the detailed emergency planning zone,” he added.