Sussex Police are spending £31,000 buying 20 Taser stun guns as a non-lethal alternative to bullets.

Tasers will not do away with the need for firearms but will replace them in last-resort situations where officers are facing violent offenders, possibly armed with knives or clubs.

The guns work by firing two probes at a target up to 21ft away. The probes contain sharp barbs and create a circuit to send a charge of 50,000 volts through the target who instantly loses muscle control and collapses.

Initially, only 60 officers trained in the use of firearms will be allowed to use them but the Sussex branch of the Police Federation believes most officers eventually will have access to them.

Tasers were first introduced in the USA where there were some concern about using electrical charges on people with heart conditions. Trials by scientists in the UK produced no lasting or long-term effects.

Assistant Chief Constable Geoff Williams said the need for less lethal options for conflict management became imperative following the introduction of the Human Rights Act.

He said: "Police are required to justify any use of force, showing it was proportionate and legal."

Other "weapons" including Captor pepper spray and batons worked well in different ways but the Association of Chief Police Officers believed the range needed extending.

Mr Williams said: "Taser does not solely rely on pain compliance. It is, therefore, more likely to be effective against a greater proportion of people than other options where deterrence or compliance is obtained through inflicting pain. It has been demonstrated where Taser has been used it has contributed to the effective resolution of the incident.

"It is not a replacement for existing conflict management options but an option that should be considered alongside others such as negotiation, batons, incapacitant spray and dogs."

The £31,000 expenditure will include training officers in the use of Taser. Running costs of the guns are expected to reach £15,000 a year. Gatwick police are to be given the same number of Tasers for use at the airport.

Mr Williams said any accidental firing of Taser would be investigated by the force and all uses would be looked into by the Independent Police Complaints Commission.

Other non-lethal weapons have been considered, including a Spiderman net-firing gun and a glue-gun which cements offenders to the ground.

Brian Stockham, Sussex Federation spokesman, said his organisation believed Tasers would be especially useful for officers under threat and waiting for back-up to arrive. He said: "We believe all officers ultimately will have access to these guns."