Oil workers are to step up the scale of industrial action in the North Sea.

Nine 24-hour strikes will be carried out across six platforms between August 15 and 31.

Another 12 six-hour stoppages will be held between August 16 and September 3, the RMT union has announced.

About 400 Wood Group employees have participated in a series of strikes over the last month – the first industrial action in the North Sea for nearly 30 years.

Unite and RMT union members working aboard Shell platforms are concerned about further cuts to pay and an unpopular switch to a three-week work cycle.

Offshore workers have been hit by a series of pay cuts over the last two years as the result of a slump in the value of oil.

High supply and low demand saw the price of a barrel of Brent crude plunge as low as $26 in January. It later climbed to $50 and now sits at about $40, a third of its price two years ago.

Oil and Gas UK believes 120,000 people in Britain will have lost their jobs in the oil industry by the end of this year.