Despite already proving their identity to airline operators before boarding, passengers on internal flights will still face routine checks by police when they disembark.

The move emerged after five Tory front bench MPs, including Chris Grayling, the shadow home secretary, were among travellers ordered to show their passports when they arrived at Prestwick Airport on Wednesday.

Mr Grayling accused police of abusing powers designed to combat terrorists and warned it was “mission creep”.

He said: “"It is utterly and completely unacceptable for any police force to be doing routine identity checks on passengers travelling within the UK.

“Do we want to end up with border check points at Gretna Green?

“Of course we need security but there has to be a balance.”

There is no blanket policy to check every passenger on domestic flights but police forces in Scotland confirmed officers do carry out checks on a regular basis.

Officers can ask someone to prove their identity and that can include showing a passport.

Strathclyde Police, which covers Prestwick and Glasgow airports, said the power was under the Terrorism Act 2000.

Currently those on domestic flights will show a form of ID to the flight operator but are rarely required to prove their identity a second time when they land, unlike those arriving on international flights who have to go through border controls.

Mr Grayling and his colleagues were flying to Prestwick to carry out some political campaigning.

He said it looked far from an occasional operation as the officer was sat at a fixed desk in the airport.

He added: “No powers should be used in this way.

“Acting like this simply undermines the credibility of our security legislation and will heighten concerns about civil liberties.”

A spokeswoman for Strathclyde Police said: “Police officers, similar to other Border and Law Enforcement Agencies, operate at UK Air and Sea Ports in furtherance of their role of protecting our communities.

“As part of their duties, Police require to establish the identity of persons present at or transiting through a Port and, in recognition of this, legislation is provided for that purpose (Terrorism Act 2000).

“In particular, specific powers are afforded to Police examining officers to require production of a passport, or other recognised identity document bearing a photograph.

“Strathclyde Police endeavour to apply these powers proportionately bearing in mind the threat levels that apply currently, particularly in respect of aviation."

A spokesman for Grampian Police, which covers Aberdeen Airport, said: “We do carry out passenger checks on both international and domestic flights and we do check identification, which could include passports."

A spokesman for Lothian and Borders Police, which covers Edinburgh Airport, was unavailable for comment.

http://www.telegraph.co.uk/news/newstopics/politics/lawandorder/6228232/Domestic-passengers-flying-to-Scotland-may-now-have-to-show-their-passports.html