THE public has a significant stake in the future plans for Prestwick Airport.

Some £25 million in investments and loans has been committed - on top of the £1 it cost to purchase to prevent its closure by previous owners Infratil.

The Scottish Government has always insisted that, as a loan, the taxpayer should view this as long-term - that a return would be achieved, but not to expect a quick solution to the loss-making airport's travails.

This is not an easy act to balance. Ministers would not want to damage rival airports like Glasgow and Edinburgh - and their owners would soon complain if public subsidy appeared to be skewing competition. Yet making Prestwick competitive is not an easy task. This is confirmed by the long awaited Strategic Vision for the airport, which has clarified ministers' plans.

The strategy is based on a report by the consultant Romain Py, which was delivered to ministers in May, but which was withheld by First Minister- in-waiting Nicola Sturgeon on the grounds of commercial confidentiality. It is odd the public cannot be trusted with any more than a mediated version of his findings, given the public funds at stake.

Nevertheless, few could argue with the overall aim - to deliver a long-term, sustainable approach at the airport.

It is probably sensible that this does not include a heavy reliance on growing passenger transport numbers.

The report describes Ryanair as the airport's scheduled passenger carrier and suggests there is no immediate likelihood of attracting other carriers to operate out of the airport.

Any likely growth in passenger numbers depends on the Scottish Government's favoured policy of cutting air passenger duty, it argues, as well as mopping up any excess demand as Glasgow and Edinburgh reach capacity. More immediate gains can be achieved by other means, ministers suggest. These include increasing charter freight and by maximising the potential of other income streams such as retail. Prestwick already has a wider range of activities than a typical airport, and it is vital this diversity is maintained, the report says.

That is all very well, but some of this is extremely speculative.

Prestwick is in the running to house the UK's planned spaceport, which the Westminster Government wants to see delivered by 2018. There are eight contenders and only two are outside Scotland. Prestwick appears to have made a strong case. A spaceport could be "the catalyst for transformational change", the document says, and it is possible to imagine not just the airport but Prestwick itself being revitalised by such a development.

However it is quite possible the Aerospace element of this vision could end up belonging to one of the other competing sites. It is true the strategy does not rely on this alone. But it is worrying for the taxpayer that without it, the prospect of a return on the investment in keeping Prestwick Airport open is a long way off.

Ministers need to clarify what action they will take in the light of it, and just how long the public must wait for it to pay off.