On Monday, MPs will vote on whether to give the third runway at Heathrow the backing of the Commons or to shelve the project indefinitely. This is a make-or-break moment in the long fight over the third runway. The chief reason the Conservatives are so confident of pushing their plans through is that they expect to count on votes from SNP MPs.

I support the SNP because it proposes and implements progressive policies standing for people and democracy in Scotland. There are several reasons why Heathrow expansion is neither social nor democratic and cannot be SNP policy.

In 2016, the SNP undemocratically signed a private “memorandum of understanding” (an agreement, to us mere mortals, though not a legally binding one) with Heathrow Airport Limited that established that the SNP would support the third runway in exchange for Heathrow offering to investigate the potential of using Glasgow Prestwick airport as a logistics hub during building, and some other unsubstantiated economic benefits. In this instance of corporate capture, the SNP has sold its vote in exchange for “magic beans”.

A new runway will exacerbate climate breakdown. Rapidly rising temperatures – we are now 1.1OC above the pre-industrial average – are causing surging sea levels and intensifying natural disasters, killing hundreds of thousands of people every year. Our dramatically disintegrating climate system is also undermining our agricultural food system, causing conflict over water and triggering mass migration. Climate breakdown is an existential threat to society.

In voting for Heathrow expansion, the SNP would push through a policy that will bulldoze homes in west London and displace residents; this is precisely the long-distance interference we rightly rail against when Westminster politicians meddle in policy north of the border. It would be profoundly hypocritical for Scottish politicians to be responsible for driving through antisocial policy in the southeast of England.

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The new runway will serve the interests of wealthy frequent flyers, not ordinary working people. In the UK, more than 70% of flights are taken by 15% of people, and these people are wealthy individuals with an annual household income generally above £115,000. Meanwhile, business flights continue to fall, as they have for more than a decade. In contrast, half of us do not fly in a given year. The driver of aviation growth is not people going on their annual holiday, it is a small number of wealthy frequent flyers. The new runway will not benefit business: it will benefit wealthy elites.

The SNP is planning to vote for a policy that will deepen inequality and damage our climate, in exchange for easier travel for the wealthiest in the UK. The SNP must think again about supporting this sociopathic policy proposed by a transport secretary in whom they professed zero confidence in a parliamentary vote earlier this week. To maintain its credibility and integrity as a progressive, environmentally conscious political force, the SNP must vote no to Heathrow.

• Jen Graham is an SNP supporter who lives in Edinburgh South West