Yobbish behaviour is costing Sussex businesses £4,300 a year.

The number of businesses affected by theft and vandalism dropped from a third in 2005 to one fifth last year, according to a survey by Royal & Sun Alliance (R&SA).

But average costs rocketed by 120 per cent suggesting acts of antisocial behaviour were increasing in severity, the Horsham-based insurance giant said.

Firms worst hit were those in the retail and consumer sectors, who saw costs rise by 80 per cent to £9,000 in 2006, compared to £5,000 in 2005.

More than a quarter of businesses in these sectors said they were affected by loutish behaviour, including broken windows, graffiti, intimidation and theft.

A similar number of manufacturers - 24 per cent - said they had experienced similar problems but with average costs much lower at just £550.

More than a quarter - 27 per cent - of businesses affected felt the problem had worsened following the introduction of 24-hour drinking legislation.

Relaxed alcohol laws were introduced in November 2005 to reduce binge drinking and violence but many of the 500 surveyed fear it has had the opposite effect.

Service sector businesses felt most affected by the legislation, with 31 per cent reporting a negative impact.

Manufacturers were least concerned.

The worst affected region was Scotland where costs averaged £4,700.

East England was least affected with businesses forking out an average of £1,600 on petty crime, with the North West also reporting relatively few problems.

Tesh Patel, corporate development director at R&SA, said: "Our research shows that although the number of cases of yob behaviour has reduced as the Government continues to tackle this problem, the financial impact is actually on the increase.

"This is a huge burden on businesses, especially on smaller companies that will struggle to cope with the financial loss."

Large businesses were most vulnerable to yob behaviour, with 40 per cent of those employing more than 200 people affected in 2006, the survey found.

In Brighton and Hove, the Business Crime Reduction Partnership has been tackling antisocial behaviour with banning orders and red card schemes for persistent offenders.

More recently, members of the Business Improvement District in North Laine and The Lanes splashed out £350,000 on security guards to patrol the area.