More than half the county's fire engines manned by retained firefighters are unusable because of a chronic shortage of crews.

A survery by The Argus revealed that 11 out of a potential 20 retained fire engines in rural parts of East Sussex were out-of-action because of the shortage on one day.

West Sussex is suffering similar problems with up to eight out of a total 44 retained fire engines off the road at any one time because of staff shortages.

Fire Brigades Union (FBU) officials are warning extreme cases like these are becoming all too regular in the county and are putting lives at risk.

Steve Huggins, of the FBU, said: "This has been going on for a long time. Ultimately, it means a longer wait for emergency attendance.

"It means full time stations are having to travel extra distances to cover these areas, adding time to their responses.

"It could also put the built up areas with whole time cover such as Brighton and Hove at risk because firefighters are being called out to cover incidents in the rural areas where retained crews are not available."

The stations without a retained crew during the daytime on Monday included Barcombe, near Lewes, Forest Row, near Crowborough, Mayfield, near Crowborough, Heathfield, Herstmonceux, near Hailsham, and Pevensey.

Full time stations, which normally also have a retained crew but could not provide one on Monday, included Lewes, Newhaven, The Ridge in Hastings, Uckfield and Bexhill.

The shortfall of retained firefighters was tested last month when emergency services responded to a serious house fire in Newick Lane in Mayfield.

Bosses had to send crews seven miles away from Heathfield and Crowborough because there were not enough retained firefighters to man the Mayfield fire engine.

A crew arrived within 14 minutes of receiving the call on January 31.

The problem of a lack of retained firefighters has emerged just months after The Argus revealed how crews were being left without any long ladders to tackle blazes because of cutbacks.

The FBU blames the shortage on the force's failure to recruit potential workers and the inflexible attitudes of employers.

Retained firefighters are paid a yearly retainer of £2,700 to be on call and receive £11 per hour when attending incidents.

The retainer has risen just £600 over the last seven years, from £2,100 in 2001.

Before the hourly wage was brought up to the same level as full-time firefighters in November 2003, the part-timers would get around £6.80 an hour whereas their full-time counterparts would earn around £10.

Since then the retained crews have seen their pay rise by just an extra £1 per hour.

They often work a full-time job alongside their emergency work. Mr Huggins said it was increasingly difficult to find employers willing to let staff leave for an emergency call at short notice.

He said: "It's a cultural change more than anything. We have to get a minimum of four people including a driver and officer to man an appliance.

"Perhaps we need to give employers an incentive."

David Lepper, the Labour MP for Brighton Pavilion, said: "Whether it's a cost issue or an issue with the specialist training needed, I'm certainly hoping to raise this with the chief fire officer.

"Across the county retained firefighters have always played an important role and I wouldn't want to see the service suffer if it's a case of a bit more money being needed to encourage people to come forward to become firefighters."

Tim Loughton, the MP for East Worthing and Shoreham, said: "This is quite worrying. Increasingly the service is relying both on full-time and retained crews.

"We need to emphasise to firms and potential volunteers the importance of a retained fire service.

"You see a few adverts for the recruitment of special constables and a lot for the Territorial Army but you don't see them for retained firefighters."

East Sussex currently employs 235 retained firefighters but the number is dropping each year and many workers are not being replaced.

In 2007, 21 retained firefighters quit at fire stations across East Sussex.

Peter Preston, the FBU's retained specialist, blamed the exodus on the hours expected of retained firefighters.

He said that when crews cannot operate due to firefighter shortages, it can have a devastating effect on morale.

Mr Preston said: "Most retained firefighters are highly motivated and they take a great deal of pride in their commitment.

"When circumstances get beyond their control it has a very demoralising effect."

He added that brigades generally have a bad history of recruiting new firefighters to replace those leaving the service through such things as retirement and this leads to more pressure on those who remain.

Retained firefighters are expected to be on call for 120 hours per week. This changed from 168 hours in November 2003.

Mr Preston said this created a shortage of cover for 48 hours a week because nothing was done by brigades to fill the gap.

He said: "There was no recruitment, no investment and no attempt made to increase the number of people covering the stations."

East Sussex Fire Authority, which funds the county's fire service, said the drop in numbers was down to changes in individuals' circumstances and firefighters moving away.

A spokeswoman said: "With changes in demographics more and more people are travelling away from home to work in the larger towns, reducing our pool of potential candidates in the daytime."

She said a new national recruitment process for retained firefighters would be introduced this year to appeal to groups that would not normally consider the role.

The authority had also relaxed the hours retained firefighters are expected to work which has helped lead to 259 fresh applicants for retained posts across the county.