Hundreds of residents have taken to social networking sites to protest against plans to change the way police helicopters operate in Hertfordshire.

More than 500 people have joined a Facebook group set up to convince the police authority to save the two helicopters that serve Hertfordshire, Bedfordshire and Thames Valley.

In an attempt to cut costs, plans have been put forward to create a national air support network of 30 helicopters to replace the existing set of individual bases across the country.

As part of the plans the Chiltern Air Support Unit Eastern Base at RAF Henlow could be closed.

Although Hertfordshire Police Authority originally agreed to the new network, changes to the plans have led it to hold off its final decision until it knows more of the details.

Concern was raised after it became unclear whether the Metropolitan Police would be involved in the national scheme. Andrew White, chief executive of the authority, said: "We need more assurance from the project team before we can agree to join. It is a way of continuing to provide a good level of air cover within the county at a reduced cost.

"We think this is an effective solution but only if we can get the guarantees we require."

The proposed plans are set to save the police service nationally £15 million a year.

According to the campaign group, under the existing base the helicopter can reach any destination in the area within 15 minutes. Under the new system, 97 per cent of the UK will be within 20 minutes flying time.

The new national service has been set up with the aim of offering 24-hour support to all forces across the country. It aims to eliminate situations that arise under the current systems where helicopters may be grounded during repairs and left unable to support the area.

Members of the campaign group are concerned that the lack of a dedicated helicopter for the area could affect crime rates in the county.

A spokesman for the group said: "The helicopter is a huge deterrent. Criminals know that without the police helicopter there is less chance of them being caught.

"I think it is the greatest single crime fighting asset.

"It really worries me that crime in the area will rise." A representative from the group met Mr White to discuss some of the main issues of concern.

Mr White said: "Many of the concerns the campaign group have, we share. I think many of our thoughts are aligned."

Once the details have been confirmed, the proposals will go back in front of the police authority, and a decision is expected to be made in June.