Justification for returning to steam a long-mothballed museum exhibit has been queried in a Freedom of Information request.

Locomotive no.16 Mannin was moved in February from the Port Erin railway museum, which has been its home for the last 20 years.

The engine is being considered for a return to steam after director of transport Ian Longworth told a UK railway magazine he wants to bring it back into service for the 150th anniversary of the railway in 2023.

A Freedom of Information request to the Department of Infrastructure asked for details of any planned overhaul, the estimated costs, and whether Treasury approval had been secured.

In its response, the DoI said the principal purpose for moving Mannin from the museum was to remove the asbestos from the locomotive.

It said during this process the loco’s overall condition will be assessed.

And until that assessment has taken place the department said it cannot give a figure for the anticipated cost of any proposed overhaul and return to steam.

There is no requirement for specific Treasury approval for this work, it said.

The FoI request also asked what the business case is for the project and what the expected economic benefit to the Manx economy would be.

In its response, the DoI said: ’The Isle of Man Railways contributed £12m to the GDP of the island in 2012 with the increase of revenue since then, this is now probably nearer £15m.

’With the increase in passengers and longer trains, we need to consider which engines are steamable based on the length of trains they can pull as we have four different sizes of steam engine.

’Similarly, some engines have worked every year and may well be in worse condition than those that have been stored for long periods and therefore we are assessing the actual condition of all the locomotives.’

Built in 1926 by Manchester-based manufacturer Beyer Peacock, Mannin was the last steam locomotive supplied to the island’s railways.

Designed to pull the heavy boat trains from Port Erin, it was the largest engine to run on the lines here.

She was withdrawn from service in 1964 and has been an almost permanent fixture in the museum at Port Erin since it opened in 1975. The only time it has been removed was during restructuring work in the museum in the late 1990s. Mannin’s place in the museum has been taken up by the island’s railway first locomotive, no.1 Sutherland, which has been cosmetically restored.