Scotland's Transport Minister has said he can not put a timescale or a cost on a possible train and tram link to Glasgow Airport.

The proposal was suggested as the best long term option by an independent study carried out by the airport and Glasgow and Renfrewshire councils earlier this year.

However, Keith Brown told MSPs that there is no plan to implement it and instead officials are looking into the possibility of such a link.

He compared the £90 million estimate to the escalating cost of the Scottish Parliament, which was first budgeted at £10m.

Mr Brown was asked about the study by MSPs on the Scottish Parliament infrastructure committee.

Labour MSP Mary Fee asked if the Government would act on the recommendations.

Mr Brown said: "The study was done by the airport. It identified short term improvements by bus.

"We are supportive of that, a bus fastlink could be achieved at low cost.

"I have asked Transport Scotland to work with the airport and the councils on the feasibility of a train/tram link."

Ms Fee asked about the cost, estimate of £92m in the report, and if that could be broken down into component parts.

Mr Brown said: "The price of this Parliament was first said to be £10m and ended up £450m.

"Cost is very indicative, we haven't broken it down. It could be short of that, it could be beyond that."

The minister said he couldn't be specific about costs or timescales, as it could be unpopular if they rose.

He added: "It would be invidious to talk about dates, like prices. There are benefits associated with it.

"The timeline, if that's what is approved, I don't think we want to be specific."

Mr Brown went on to speak about the importance of flights to London airports and problems at Heathrow.

He warned that Heathrow had to serve the rest of the UK as well as the long-haul flights that earn more cash and criticised the UK Government over Air Passenger Duty.

He said: "APD is an inhibitor to routes from Scotland, having to pay twice to get from a hub to Scotland.

He said there were difficulties because long-haul flights were prioritised because they were more lucrative.

He added: "If they want to be the hub airport they have to act like one, and not have the highest APD in Europe."

He said Scots can fly to the USA and to Dubai via Dublin and avoid APD.