A shortage of sergeants is threatening to send Sussex Police into crisis.

There are currently vacancies for 60 but there are only 24 PCs eligible for promotion to the posts.

The police federation said the situation was putting intolerable strain on sergeants in post.

The main reason for the shortage is the difficulty of the exams PCs have to take for promotion to the rank but the "brain drain" is also a problem.

Some officers are leaving Sussex to join other forces, mainly the Metropolitan Police which pays £6,000 a year more and provides free travel.

Chief Constable Ken Jones this week repeated a call to those thinking of leaving to talk to him first.

His email, leaked to The Argus, said: "Over the past year or so I have personally seen many officers who were considering transferring to other forces or leaving the service.

"I'm writing to let you all know that my offer stands. I will do whatever I can to hold on to good people. Sussex is a great place to live and work.

"If you are thinking of leaving us then please email me.

"Incidentally, in the year to March, 2003, we lost 72 of our colleagues and gained 32 from other forces. A net loss of 40.

"Despite our losses, our overall police numbers have now returned to 1996 levels after an unwise period of significant contraction.

"Our net loss of 40 is nowhere near as bad as Surrey, Bedfordshire or Thames Valley are experiencing and we should all work had to make sure we continue to contain this."

Five more officers transferred out of Sussex in April, two to London, and six have gone this month.

A total of eight transferred into Sussex during the same period.

One officer responding to the chief's email told The Argus: "Is this not the action and words of a desperate man?"

The officer, who declined to be named, said many more colleagues were considering leaving the force and morale was low.

But Graham Alexander, of the Sussex branch of the Police Federation, said morale was still recovering from the years under former chief Paul Whitehouse.

He said: "Make no mistake, Ken Jones is a good chief but he can't undo this overnight. It will take a long time."

In the meantime, he said, the "nightmare" promotion system needed an urgent overhaul.

He said: "Sergeants play a crucial hands-on role and it is a crying shame they are suffering this additional stress and pressure due to lack of numbers.

"But this is a national problem."

A federation survey showed the numbers of sergeants nationally had fallen more than 1,000 in ten years.

The exam system, it said, was so arduous that many PCs did not bother to seek promotion.

They had been put off by the "hoops they have to jump through".

The federation described the sergeant rank as the "foundation of the service" and it is demanding changes at promotion board level.