The major evacuation of all 115 workers from the EnQuest-operated Thistle platform in the UK northern North Sea on Monday is “unprecedented”, according to an Aberdeen-based trade union leader.

RMT regional organiser Jake Molloy told Upstream he was unaware of a North Sea facility being downmanned for structural integrity reasons at such speed.

“This was a complete abandonment at significant speed. I’ve been around the industry for a long time and to do that for reasons related the structure of a platform is unheard of. It’s unprecedented,” said Molloy.

"It’s possibly unfair to speculate at this early stage but if an operator has a robust inspection regime then you should not be needing to downman a platform like this."

EnQuest "proactively downmanned" Thistle, located about 200 kilometres north-east of Shetland in Block 211/18, in what it called a "precautionary move" on Monday.

This followed an inspection of a support element on a redundant subsea storage tank.

The platform has been known to workers for years by its nickname "The Black Pig".

A UK coastguard helicopter from Sumburgh in Shetland was assisted by two other aircraft from Norway to transfer the personnel to the nearby Dunlin Alpha platform.

EnQuest said later on Tuesday that workers were flown to the nearby Dunlin Alpha platform and are now in the process of being transferred home.

Molloy called into question EnQuest’s use of the word “precautionary”.

“Precautionary would normally imply having time to carry out some planning and the use maybe of some scheduled or routine helicopter flights to take staff off in a controlled manner. Often a group essential staff would be left on board also," he said.

"So, to use the word ‘precautionary’ in this instance — a complete abandonment done quickly — does not seem to add up.”

Molloy referred to CNR International's decision to take staff of the Ninian South facility n late-2017 ahead of poor weather amid concerns about the structural integrity of the jacket".

"Even that was controlled," he said.

Molloy also called on EnQuest and the North Sea industry to be as open as possible in sharing details about what has happened at Thistle.

“We keep hearing from the industry about the need for learnings, sharing and openness.

"Well, there are a number of jacket-based platforms in the North Sea are of this advanced age.

“If there are learnings to be gained from what happened on Monday, let’s hear about them and share them with the operators who have those older platforms.

“EnQuest should tell us what is going on. Being open will help to dispel any speculation.

“We have got to be clear about what has happened, why it has happened and how to remedy it.

“That will build confidence among the workforce, their families and the wider public.”

The Health & Safety Executive (HSE), the UK safety regulator, said has said it is aware of the evacuation and is making further inquiries.