Governments that fail to implement much-vaunted manifesto commitments inevitably suffers at the polls.

Just look at the Liberal Democrats who continue to be punished by voters over their failure to honour a commitment to scrap tuition fees as part of the 2010-15 coalition government.

The SNP’s U-turn, this week, on a promise to half Air Departure Tax (ADT) not only looks like the worst kind of opportunistic virtue-signalling by Nicola Sturgeon, it also threatens two of Scotland’s most important industries.

Tourism has made huge strides in recent years, making Scotland one of Europe’s most visited destinations, but it has only done so by being competitive. It’s no accident that a 27% increase in visitor numbers and a 20% rise in tourism spending last year coincided with a weakened pound.

Overseas travellers are among the most price-sensitive of all consumers and, in normal circumstances, being asked to pay one of the highest air passenger duties in the world is a significant disincentive for many.

Reversal of the proposed £150million tax cut could also have implications for the airline industry and we’ve already seen how capricious companies like Ryanair can be.

Last year the Dublin-based airline reduced the number of scheduled flights from Glasgow from 23 to just three because of the Scottish Government’s back-peddling on a commitment to replace ADT with a cheaper air passenger duty.

Ministers were then still insisting they remained committed to reducing ADT by 50%, after resolving several unspecified issues, and their failure to do so might yet lead to further cuts.

It was noticeable that this week’s announcement was made by Roseanna Cunningham, the environment secretary rather than ministers for tourism, business or finance.

Nicola Sturgeon’s declaration of a ‘climate emergency’ was given as the reason as she revised emissions targets further downward, making them the most stringent in the world.

“All parts of government and society have a contribution to make to meeting this challenge – and reducing Air Departure Tax is no longer compatible with more ambitious climate targets,” said finance secretary Derek Mackay.

All very laudable but the same ministers faced the same climate change challenges ahead of the last election as they brainstormed eye-catching policies to win support from the same voters whose jobs they’re now threatening and whom they’re penalising with higher taxes and less choice of where to fly on holiday.

Most, if not all, people in Scotland will welcome the strictest measures to combat climate change so they may be baffled by the Scottish Government’s continued support for cuts in ADT at Inverness Airport and a £40million and rising subsidy for the failing Prestwick Airport.

They may agree with Edinburgh Airport chief executive Gordon Dewar who said such a contradiction amounted to “hypocrisy”,  adding: “It not only punishes families and those who work hard to afford a holiday by enforcing one of the highest aviation taxes anywhere in the world, but will restrict our future connectivity, investment into Scotland and job creation as we sacrifice Scotland’s international outlook.”

They might also agree with Chic Brodie, a former Nationalist MSP for the South of Scotland who accused the first minister of “headline hugging” and said her policy switch “appeared to have been made in ignorance of work being done in the aerospace industry on reduced emissions.”