Air traffic controllers in the Highlands and Islands have rejected a revised offer amid strikes over pay.

Prospect union members took industrial action in May and were scheduled to walk out again on June 12, but called off the strike after Highlands and Islands Airports Limited (Hial) put forward a new deal.

However on Friday, it was announced that the proposal was "overwhelmingly" turned down.

Although further strike action has not been announced, employees will "work to rule" from Saturday - which includes an overtime ban, an instruction to work to rosters and the withdrawal of good will.

Prospect and Hial will meet again on Thursday, July 4 in a further attempt to resolve the dispute.

David Avery, Prospect negotiations officer, said: "Prospect members in Hial have overwhelmingly rejected the revised pay offer made by Hial.

"The work to rule which was suspended during the ballot will restart tomorrow.

"Prospect will meet with representatives on Monday to consider the ballot result prior to a meeting with Hial on Thursday, July 4 to try and resolve this dispute and reach an offer which is acceptable."

A strike in April disrupted services at Inverness, Dundee, Benbecula and Stornoway in the Outer Hebrides, Sumburgh in Shetland and Kirkwall in Orkney.

Prospect claims members' pay has fallen significantly behind the rest of the industry due to public sector pay restraint.

The union is looking for a 10% pay increase.

The controllers had been working to rule since the beginning of April.

Amid the dispute, a plane was forced to depart from Orkney to Edinburgh without air traffic control clearance.

The union argued that start-up clearance was denied as it would have involved a controller having to work beyond their shift - contravening "very strict" rest periods.

Hial, a public corporation wholly owned by Scottish ministers, previously insisted it was bound by government pay policy and could not negotiate a separate settlement.

However, the Scottish Government permitted Hial to develop a retention allowance in a bid to resolve the dispute.

Inglis Lyon, HIAL's managing director, said: "We are obviously disappointed that our latest offer has been rejected by air traffic control officers, despite enhancing our formal offer following last-minute discussions with Prospect.

"It is unfortunate that the industrial action has been reinstated during the peak holiday period and I would like to apologise in advance to our passengers, customers and local communities for the disruption this will inevitably cause.

"The offer was made within the parameters of the Scottish public pay policy in a bid to resolve the dispute to the satisfaction of both parties.

"We have encouraged Prospect to meet and discuss an alternative solution within the flexibilities afforded to the company.

"We remain committed to resolving this dispute and a meeting with Prospect will take place on Thursday, July 4."