The three-week trial has been prompted by motorists parking dangerously on some of the city's busiest roads, possibly aware that no wardens are on duty at night.

Drivers face having their cars impounded and a £30 fine if they are caught by the patrols, which will operate from 6.45pm until around midnight.

Police say they are responding to complaints from residents, taxi drivers and bus companies. Cars left on the double red lines, which don't allow parking at any time, have often blocked bus stops or put pedestrians in danger.

The trial begins from Monday, but Lothian and Borders police chiefs today said they would continue if problems persist.

Residents today welcomed the crackdown but wardens said staffing the patrols would be an issue if they become permanent.

Inspector David Begge said the worst problems were in city centre areas such as Lothian Road, where many motorists leave their cars during a trip to a restaurant or theatre. He said: "This trial is just a gentle reminder to drivers that parking on the double red lines is dangerous.

"It is more aimed at the social driver who is maybe coming into the centre for a night out and leaves the car in the Greenways because they think it is not doing any harm.

"We have had concerns raised about this issue and in particular we are worried about pedestrians having to navigate between cars parked dangerously."

The number of police-employed traffic wardens in Edinburgh will be cut from 58 to 27 on July 2nd, ahead of responsibility for the Greenways being handed over to parking attendants from the council's private firm NCP later in the year. Wardens typically patrol the city's streets between the hours of 8am and 6.45pm Monday to Saturday. The night-time Greenways patrols, which will initially operate between Monday and Friday, will be offered to existing wardens as overtime.

One senior warden, who asked not to be named, said: "This was news to us as the wardens weren't aware of a big problem after hours. However, if they try to put this in longer term then I think they will be struggling because we won't have the numbers."

David Rintoul, chairman of Tollcross Community Council, said: "This is very welcome and long overdue. A little shock from the wardens will hopefully do the trick. I think some drivers think the road rules finish when the wardens do, so hopefully it will bring a bit of order back to the streets.

"You even have them parking on these double red lines on corners, it is really dangerous and a hazard for pedestrians trying to cross the road."

Bill Campbell, Lothian Buses operations director, said: "It is encouraging to hear that the number of police traffic wardens will be increased and on hand to prosecute those who block vital bus lanes, Greenways and bus stops.

Yesterday, the News revealed drivers also face the prospect of mobile speed cameras around the Capital working longer.

The Greenways tend to be in operation for most of the day, not just peak hours, and double red lines indicate an area where it is dangerous to park and are enforceable 24 hours a day. Drivers are not allowed to park, load or unload vehicles.