THE Scottish Liberal Democrats have asked for £400m of investment in return for helping the SNP pass its budget.

Leader Willie Rennie last night demanded £70m more for schools, £93m for colleges, and £20m for the police, as well as cash for mental health and cheaper transport to the LibDem seats of Orkney and Shetland.

The move marks the start of serious horse-trading between the SNP and the other parties in the run-up to the crunch vote at the end of February.

Read more: David Mundell dismisses SNP Brexit plan ahead of Whitehall showdown

The Government has 63 votes, two short of a majority, making it reliant on at least one other party at Holyrood to support its budget bill, or to abstain.

With the Tories and Labour politically unacceptable to the Nationalists, finance secretary Derek Mackay is likely to deal with either the LibDems (five votes) or the Scottish Greens (six).

However Green demands for more radical taxes may be a problem for the SNP.

In a letter to Mr Mackay, Mr Rennie said he was asking for “a tight and prioritised list that has the long term future of the Scottish economy at its heart”.

He said it was smaller than the proposals in the LibDem manifesto last year, which suggested raising an extra £500m by adding a penny to every rate of income tax.

Read more: David Mundell dismisses SNP Brexit plan ahead of Whitehall showdown

Mr Rennie said he was ready to discuss the matter further with Mr Mackay, but said LibDem support would require “significant and substantial change” on the issues his party had identified.

He said “The SNP have no majority for their draft budget. If they want a majority they will need to agree to this comprehensive but necessary plan.

“Liberal Democrats will not agree to the draft budget as it stands and will need these substantial changes. If we don’t get what the country needs then we will walk away.”

Before the draft budget for 2017-18 was published in December, the Scottish Greens said they wanted it to be “anti-poverty”, with greater investment in schools, GPs and public services.

They also wanted “movement on tax policy”, instead of the SNP “sticking rigidly to their own manifesto position”, which made incremental changes to council tax and income tax.

Last week Green MSP Patrick Harvie also suggested topping up child benefit by £5 a week.

A Green spokesman said: “Many of the spending plans the LibDems are putting forward will be widely supported. The question is how it’s to be paid for.

“We have set out ways of protecting everyone on a low or middle income, and ensuring that the tax system is more progressive.

“The Lib Dems have never explained why they think Basic Rate taxpayers should foot the bill, which would cut the take-home pay of people who’re already struggling on low incomes.”

Read more: David Mundell dismisses SNP Brexit plan ahead of Whitehall showdown

A Scottish Government spokesperson said: “The draft budget prioritises growth and public services and includes new investment in healthcare, education and local services, combined with support for jobs through lower business rates.

“We will continue to have discussions with the different parties across Parliament as we take forward our plans for a fair budget which delivers for Scotland.”