The majority of Scots would no doubt agree with SNP deputy leader Stewart Hosie when he says that whichever of London's two main airports can offer Scotland the best direct flight connections should win his party's backing for its expansion plans.

Heathrow and Gatwick Airports have both made pledges in relation to Scotland in the past and are renewing them as the respective campaigns lobby SNP politicians in Aberdeen. The Davies Commission has recommended expanding Heathrow with a third runway at a cost of £19bn, but the UK Government is still considering its response.

Mr Hosie said the airport most likely to offer flights to Scots 'in abundance' will be supported by the SNP.

London's airports are key gateways to international travel for Scotland. That situation will not change dramatically even with the devolution of Air Passenger Duty, which the Scottish Government could vary to encourage more direct flights to and from Scotland.

There are environmental questions surrounding any reduction in APD, of course. Worldwide, we should be looking to reduce air travel where possible, to help tackle climate change. Passenger numbers at both Glasgow and Edinburgh airports are already soaring.

But airline taxes in the UK are the highest in the world, and Heathrow and Gatwick are likely to remain vitally important hubs connecting Scotland to the wider world.

The issue then becomes how well Scotland is connected into those hubs and it is here that the rival pledges are particularly important. Gatwick has promised a £20m fund for regional connections if it wins its bid to build a second runway. Heathrow has pledged better timed and more frequent flights to airports already served, as well as a fund to help set up new links to cities like Dundee.

There is a danger that expansion could see fewer rather than more connections as we have reported before. A third runway at Heathrow, for example, could see an increase in demand for new slots squeezing domestic routes.

It is good news in this context that Aberdeen-based First Group are still intending to launch a low cost rail service between Edinburgh and Lndon, in a bid to lure passengers away from air. But airport links will still matter.

All this lobbying comes because the SNP's block of MPs is potentially pivotal in a close-fought decision at Westminster. Forget the bluster of some English MPs that their Scottish counterparts should abstain on any votes over the decision, or that it would be undemocratic for favourable terms to be offered to Scottish travellers in return for votes. Scottish MPs are elected to stand up for their constituents' interests and there is nothing wrong with that. However they should take such a decision based not just on fares, but all the relevant factors including the prospects for jobs and growth, better access to export markets and internal connections.

SNP politicians being sweet-talked by the airports should remember too that what is offered now must also be delivered later. Whichever airport wins the right to expand, its management must be held to their promises.