The crew of the ship towing an oil rig that ran aground in a storm failed to plan for bad weather, it has emerged.

The 17,000-tonne Transocean Winner washed up on Lewis in August 2016 after breaking free from the tug ALP Forward.

Her fuel tanks ruptured when she hit land and 53,000 litres of oil spilled into the sea, though the pollution dispersed harmlessly.

It cost Transocean nearly £17m to retrieve the rig from Dalmore Bay in an operation that took two weeks.

A newly released report reveals the crew of the ALP Forward did not plan properly for bad weather during the Winner's journey to Malta, where it was going to be broken up for scrap.

ALP Forward was incapable of controlling the ageing rig in stormy seas, the Marine Accident Investigation Branch (MAIB) said.

The tug was dragged backwards by the Winner for more than 24 hours after losing control of her in 50mph winds and 55ft waves off Scotland.

The officer in charge of planning the journey did not take the weather into account, the MAIB said, and there was no contingency in place.

The crew of the Transocean Winner would have ballasted her down in a storm but Transocean decided to tow the rig unmanned because it was cheaper.

The MAIB said it could not speculate on what might have happened if the rig had been crewed.

The master of the ALP Forward was also unaware of the Winner's windage - its wind resistance - a crucial piece of information.

The MAIB noted: "Had the information been available, the master would have been able to predict the tug's inability to hold the rig, enabling him to change his plan in time to seek shelter."

A spokesman for ALP Forward owner ALP Maritime Services, said its crews are "some of the best trained and most experienced in the industry".

They added: "ALP is currently studying the conclusions of the MAIB report.

"Once reviewed we will take any lessons that can be learned from the investigation and our own internal findings on board.

"Meanwhile, ALP would like to emphasize that safety remains our number one priority and we are fully committed to ensuring that all equipment used is fit for purpose at any time"

The grounding of the Transocean Winner led to renewed calls for an emergency tug based in the Western Isles.

Scotland's only emergency towing vessel (ETV) has been docked in Orkney since the Stornoway tug was scrapped six years ago.

The MAIB said it is "very unlikely" a local tug would have been able to prevent the grounding, however.

A spokesman for Transocean said: "Transocean remains grateful to all who provided assistance last summer.

"We will continue to meet our responsibilities arising out of this incident and appreciate the Marine Accident Investigation Board's review and recommendations.

"For the past year and continuing through this August, Transocean has conducted regular surveys and inspections of the beach and grounding site, where no pollution has been detected.

"The Transocean Winner was sold in 2016 for recycle in an environmentally responsible manner, with the recycling project completed early this year."