Capacity at the site just off Eastfield Road has been more than doubled to 1085 spaces with the completion this week of an £2.7 million extension.

But airport bosses today warned the expansion will place further strain on the roads into what is now Scotland's busiest airport.

They are pressing for new road links to their terminal because of concerns the 1960s-built, two-lane Eastfield Road is barely coping with the demands placed on it by traffic heading to the airport.

The original Ingliston site has been operating near capacity since it opened in 2005.

Council chiefs today said they are installing signals on the roundabout next to the park-and-ride to improve management of the increased traffic flow.

But airport chiefs said the expansion will only add to the traffic build-up at an already busy pinch point.

A spokeswoman for airport operator BAA said: "There is little doubt that the expansion of the park-and-ride facility will place further strain on what is already an overloaded road network.

"We have already seen how congestion on the A8 and Eastfield Road can bring traffic coming to or going from the airport to a standstill.

"This further strengthens the case for investment in new roads in the area While we are committed to increasing the number of our passengers who travel to and from the airport by public transport, good road access for our growing number of passengers continues to be vital."

The network of park-and-ride sites surrounding Edinburgh means there are now more than 3500 spaces for drivers to leave their cars at Ferrytoll, Newcraighall, Hermiston, Ingliston and Sheriffhall.

The opening of another at Straiton later this year will see this number rise by a further 600.

Councillor Phil Wheeler, the city's transport leader, said: "One third of Edinburgh's workforce travels to work from outwith the city. By providing secure, free parking and comfortable, efficient, fast bus services from the outskirts of town we are giving drivers a good alternative to taking their cars into the city centre.

"Along with the new site at Straiton, due to open in the autumn, we are currently looking for additional sites along the city boundary. That way we can further help ease the daily commute for thousands of drivers while doing our bit for reducing congestion and pollution."

A total of 100,000 cars used Ingliston and Hermiston park-and-ride in their first six months of operation.

• www.edinburgh.gov.uk