More than 70 officers have left Sussex Police in the past year to earn more money with the Metropolitan force in London, the biggest loss in its history.

And there is no sign yet the "brawn drain" is ending.

Sussex has attracted some transferees and a recruitment drive has bolstered the force's overall strength to a record 3,100. But it will take time to recover the experience lost.

More than 500 Sussex officers are still in training as probationers.

Many of those who transferred out were experienced officers, such as Steve Wagstaff, a detective inspector in charge of the intelligence-gathering unit at Brighton police station.

Graham Alexander, of the Sussex branch of the Police Federation, said that kind of experience couldn't be replaced overnight.

He said: "It is the old adage - you can't put old heads on young shoulders."

Mr Alexander said he expected defections to continue for another month or so and warned: "If the brain drain continues, it could be catastrophic for the force."

Chief Constable Ken Jones, in a report to the Sussex Police Authority, said 72 officers had left in the past 12 months and 27 had transferred in.

He said the force's efforts to increase numbers to their highest point ever was a "creditable achievement".

The force wants to further increase its strength to 3,140 by next April. To achieve that, it will need to recruit 350 to allow for retirements and transfers.

Sussex officers who left for London have been tempted by an extra £6,000 they can earn, plus free travel.

Sussex is trying to fight back with an advertising campaign aimed at wooing officers who currently commute to London.

The force is also planning to entice back to work up to 30 retired officers, as well as experts in computer and finance crimes to beef up investigations.

It has also negotiated free bus travel for officers in Brighton and Hove.