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Nicola Sturgeon’s minority government has dropped plans to cut air passenger duty in Scotland by tens of millions of pounds from next April at the same as it wrestles with significant problems funding its election promises, particularly lifting the public sector pay cap and a £500m plus inflation increase in health spending.

In a footnote to yesterday’s UK budget papers, the Treasury said it had agreed to Scottish government requests to postpone the devolution of APD from 1 April 2018, so the UK government will continue to control the tax in Scotland, paying Holyrood its share through the block grant.

The Scottish National party had pledged at successive elections to cut the tax, which it was to rename air departure tax (ADT), by 50% or about £189m by the 2021 Holyrood election. But it also promised far higher NHS spending and to increase public sector pay by more than 1%, while dealing with cuts in its Treasury grant.

According to Unison, the public sector union, raising public sector pay 2% across the board in Scotland would cost £380m and by 3%, £560m. Unison and the PSC civil service union want a 5% rise.

Derek Mackay, the Scottish Finance secretary, told The Herald he had called the Treasury on Tuesday to seek postponement. In early October he blamed the latest EU rules on state aid for his delay in a decision of ADT, which would apparently prevent the Scottish government from keeping a “life line” exemption from APD for flights to Scottish islands in place since 2001 if it changes air duty.

But crucially for Mackay and Nicola Sturgeon, the deal will help relieve intense pressure on the Scottish budget which will be unveiled on 14 December and reduce the need for Sturgeon to call for higher taxes. It is thought Mackay faced a £600m spending black hole earlier this autumn, which the chancellor’s budget yesterday has helped slightly relieve.

And cancelling an ADT cut will also make it much easier for the Scottish Green party to vote for this budget: they had pledged to vote against it if air duty was cut. The SNP is three votes short of a Holyrood majority: six Green votes give it a much needed cushion