An investigation is under way after problems developed in one of the legs of the jack-up Noble Hans Deul, prompting the crew to be called to muster and halting development drilling work at a field operated by UK gas company IOG.

IOG said the problems occurred during a "routine jacking operation" early on Sunday 10 October after the unit had recently arrived at the Southwark field from the Blythe field, which both form part of the company’s Saturn Banks project.

No drilling was taking place at the time.

IOG said the rig went to full muster while the issue was assessed and all 66 people on board are safe and well.

There was no damage to the rig hull or to the Southwark platform and the unit is now stable and secured by tow boats while the crew assesses its condition.

IOG said its priority is the "safety of all staff, ensuring the rig's integrity and the safe and efficient continuation of the drilling at the earliest feasible time".

Rig owner Noble Corporation has started an investigation into the cause of the issue.

It is initially expected that the rig will be transported to port for insections before drilling can be resumed, IOG said.

The company said it continues to expect first gas from both the Blythe and Elgood fields in the fourth quarter this year once final subsea and onshore installations are complete.

IOG chief executive Andrew Hockey said: "Needless to say, we will be taking all necessary actions to minimise the interruption to safe and efficient development drilling at Southwark caused by this unexpected issue identified by the Noble Hans Deul rig during jacking operations.

“Most importantly, there has been no harm to any personnel or any IOG assets. In the meantime, this has no bearing on the timing of Phase 1 first gas from the Blythe and Elgood fields which remains on schedule to occur during Q4 2021."

A spokesman for Noble Corporation said: “Our priority is the safety of our people, those working alongside us, and ensuring the integrity of our vessels and their operations.

"An issue which affected braces on one of the jack-up legs of the Noble Hans Deul was detected following the vessel’s arrival in the field ... No drilling or associated operations were ongoing at the time.

“ The drilling rig is stable and connected to tow boats. The crew is carrying out initial assessments ahead of transportation to port for repair.”

Upstream understands the UK Health & Safety Executive (HSE) have been informed about the incident but it is currently unclear if the regulator will be investigating.

Saturn Banks is the new name for IOG's Core project.