A deal has been made to ensure foreign sailors serving aboard Northern Isles freight boats are paid at least the minimum wage.

Protests were held in Aberdeen over reports crewmen on ferries sailing under a Scottish Government contract were earning as little as £4 an hour.

The Northlink-owned vessels had been subcontracted to Irish ferry firm Seatruck, which refused to pay the minimum wage.

It is legal to pay sailors less than the basic rate as long as they are recruited overseas.

But RMT union organisers branded the service a "ship of shame".

General secretary Mick Cash said: "After years of behind the scenes pressure by RMT officials, and high-profile campaigning last year, RMT is delighted that at last the Scottish Government have publicly stated they will pay at least the national minimum wage on the contract.‎"

The contract run by Seatruck is expected to return to Northlink next month.

Transport minister Humza Yousaf said: "The current situation with crew being paid less than the minimum wage is unacceptable and as soon as I first became aware of it, I gave a direct commitment to meet with Seatruck in person.

"I'm very pleased to see an agreement in principle now in place to end this long running issue around the freight vessels serving the Northern Isles."

The new agreement will not affect the majority of foreign seafarers employed in the North Sea, although the UK Government is also reviewing maritime employment legislation.

At times more than half of the foreign-flagged vessels contracted by the oil and gas industry reportedly employ crew on less than the minimum wage of £6.70.

Some seafarers are allegedly paid as little as £2 an hour.

"Ship owners cut their wage bill by getting rid of UK seafarers because they are able to discriminate against foreign seafarers by paying them less," Mr Cash said.

"Every day seafarers including those working on vessels chartered as part of a public contact for services between UK ports - continue to be exploited by rates of pay well below the UK minimum whilst shipowners enjoy massive tax breaks and a complete lack of accountability."

A back bench parliamentary debate on the issue will be held at 3pm on Thursday.