THE SNP yesterday promised to begin moves to renationalise rail services within Scotland if it won power in the May 1 parliamentary elections.

The party revealed long-term plans to create a Scottish National Railways Authority, which would include track and train operators.

However, political opponents poured scorn on the idea, claiming it was yet another ''misleading spending promise'' and showed the Nationalists were ''anti-profit''.

As a first step towards the SNP's goal, which would need legislation at Westminster, Kenny MacAskill, transport spokesman, pledged to replace the existing ScotRail operating franchise with a not-for-profit trust.

The franchise, which is currently operated by National Express, is due for renewal next year. The retendering process has already begun and several possible operators have shown an interest.

The SNP spokesman stressed no contracts would be signed or entered into before the May election. He added that the ScotRail franchise was not a big one in UK terms and was unlikely to see any significant investment through an incoming operator. The new trust could reach bilateral agreements with cross-border operators such as GNER

and Virgin.

At a press conference in Edinburgh, Mr MacAskill said: ''It is time to take our train network back into public hands.

''The Tories' privatisation has been an unmitigated disaster, both in terms of service to the customer and cost to the taxpayer.''

He said the next stage was to take the ScotRail franchise back into the public sector using the same model.

If it was ''sensible and practical'' to run the track operation this way, it was just as sensible and practical to do so for the train operator, claimed Mr MacAskill.

Such a move would be the first step towards fully integrating Network Rail, the Strategic Rail Authority, and the not-for-profit train operator into a Scottish National Railways Authority. By introducing the new trust at the time when the current franchise ran out in April 2004, Mr MacAskill argued that the move would be ''cost neutral''.

But the Scottish Liberal Democrats seized on his claim as ''another misleading spending promise'' and accused the SNP of playing games with taxpayers' money.

Nora Radcliffe, the party's spokeswoman, said: ''The SNP fails to explain how 126 diesel trains, 104 electric trains, and 74 sleeper carriages - including 66 new trains worth (pounds) 200m - are to be transferred to public ownership for free. ScotRail train rolling stock costs (pounds) 55m a year to lease and is worth hundreds of millions of pounds.''

The Scottish Tories were equally dismissive of the SNP's plans, claiming the ''ludicrous'' proposal showed the party's true left wing colours.

Tory spokesman David Mundell said: ''They masquerade as a pro-business party, but their socialist dogma and default 'public good, private bad' approach always rears its ugly head when it comes to the crunch.''

The executive insisted ''disintegration'' of the rail network would not be in the interests of Scotland's travelling public.