The leak on the Elgin PUQ platform, about 150 miles off the coast of Aberdeen, led to the evacuation of all 238 workers. Total have also stopped production and part-evacuated its nearby Franklin platform.

The company said that it could take as long as six months to drill a relief well to stop a gas leak at an offshore platform.

Shell also evacuated workers from one offshore installations nearby as a 'precautionary' measure.

Jake Molloy, Regional Organiser of the OILC union, told STV that there may be a risk of explosions and of the poisonous gas hydrogen sulphide, although added that the evacuation had been quick and efficient.

Mr Malloy, has said that the slightest spark could trigger a massive explosion at the Elgin PUQ rig in the North Sea. He said that engineers were dealing with an unprecedented situation since gas is leaking from outside the casing walls.

Total has flown in 10-20 specialist engineers to tackle the leak and enlisted the services of Wild Well Control, which was heavily involved in the BP's Deepwater Horizon oil spill in the Gulf of Mexico in 2010.

David Hainsworth of Total E&P UK, which operates the Elgin PUQ oil rig, admitted that the release of gas could go on "for a significant period of time". He said:

The gas is flammable but the platform power was turned off to minimise risk of ignition, but clearly there is a risk. We have taken away a series of risks but there is always a possibility, it's low but you never say never. The best-case scenario is that the gas in this area is not very productive and it dies off in the coming days and weeks. At the moment there is no real evolution of the sheen on the sea but if that was to change - and it's monitored on a daily basis - then the exclusion zone may be increased, but at the moment it will probably stay the same.

Elgin PUQ platform Credit: Reuters

Dr Martin Preston, marine pollution specialist and research fellow at the University of Liverpool has said that a gas leak at one of operator Total's offshore platform could harm marine life. Dr Preston said that the process to drill a relief well may take months. He said:

The gas in this field is 'sour gas' - it contains hydrogen sulphide which is very poisonous to humans and aquatic life - so localised risks to marine life are likely