Delivery of the long-delayed Glen Sannox ferry has been pushed back once again, MSPs have been told.

The Ferguson Marine shipyard said it had been forced to postpone a key test of its liquefied natural gas (LNG) fuel system.

The state-owned shipyard found the process of cooling the pipes to the sub-zero temperatures necessary to load the fuel was taking longer than anticipated.

This meant they would no longer be able to meet the deadline for the handover to the ferry-owning agency CMAL by 30 September. The latest delay is expected to be approximately two weeks.

The ship and its sister vessel, Glen Rosa, were originally due for delivery in 2018 but have faced repeated design and construction challenges.

Both ferries were designed from the outset to be "dual fuel" ferries, able to run on both traditional marine gas oil and LNG.

But problems installing the LNG system have been behind some of the repeated delays in delivering the two ferries, with the Port Glasgow shipyard dealing with these issues over the past year.

Ferguson Marine's interim chief executive John Petticrew wrote to MSPs to inform them of the latest delay.

He said: "The past week has seen us dealing with several technical challenges relating to the cooling of the LNG system, which has delayed the loading, final commissioning of the system and the harbour and sea trials.

"Regrettably, this means that some of the work required after these trials will not be completed in time for the proposed handover at the end of September 2024."

Mr Petticrew added: "I am personally very disappointed to be delivering this news, but I can assure (you) that the team at the yard are doing everything possible to keep as closely as possible to the proposed schedule."

LNG needs to be kept at below -160C in order to remain in a liquid state.

Following the harbour trials, the plan is to put the vessel through its paces at sea, stopping and starting several times and carrying out endurance tests.

Current cost estimates for Glen Sannox are between £145.5m and £149.1m and it is hoped the cost of Glen Rosa will be kept below £150m.

Now six years late, the total bill will be three times the original £97m price tag.

Glen Sannox undertook sea trials earlier this year, but in those tests the 102-metre vessel was not using LNG.

The ferry, which has capacity for 852 passengers, is designed to serve the Arran route with CalMac.