It's going to cost us about �200 plus in paint, it's going to cost us the time of the three men we have to send there

James Taylor, Chief Executive, NLB

Speaking on BBC Radio Scotland's Newsdrive programme, James Taylor, Chief Executive of NLB, said: "It's not a laughing matter because right now we're having to go out there and restore it to its original condition.

"That takes time, that takes effort, that takes money.

"I'm sure some people think this is pretty amusing stuff but it's the equivalent of perhaps painting out traffic islands or the roundabout.

"It is the equivalent perhaps of interfering with the points on the railway line.

"We're dealing here with something that provides a safety system for mariners.

"We're just treating it as a piece of ridiculous and mindless vandalism."

'Less visible'

Mr Taylor said the pink paint would make the lighthouse less visible to seamen most of the time and less effective as a piece of safety equipment.

"It's going to cost us about �200 plus in paint, it's going to cost us the time of the three men we have to send there," he said.

Officials warned of a possible threat to shipping

Mr Taylor confirmed that white paint had already been sent to the Port Appin lighthouse by helicopter and the total cost of repair was likely to run into four figures.

He said that as a result of the vandalism, the NLB had issued a "Notice to Mariners advising of this change of status".

Mr Taylor also said that the matter was now in the hands of Strathclyde Police and the NLB would seek to recover the cost of repair from whoever was responsible for the vandalism.

The NLB said the lighthouse's sudden change in appearance was reported to officials at its depot in Oban by a local resident and was confirmed when personnel visited the site.

Plans have been announced to replace the gas-powered lighthouse with a reinforced glass structure running on solar power.