A perimeter fence four metres high and topped with electrified wire is to be built around the 240-hectare London Olympic Park this year, Games authorities said yesterday.

The wire-mesh fence, designed to allow people to watch construction of the Olympic facilities, will have a 5,000-volt “power topping” to act as a deterrent against unauthorised entrance. Details of the fence were given as the Metropolitan Police said that more than 1,500 police officers would have to be seconded from other forces to ensure adequate security for the 2012 Games.

Retired police officers might also have to be brought back into the service and specialist staff kept on after their retirement date until the Olympics were over. More explosives sniffer dogs and horses for mounted police would also be needed from other forces and the Army.

David Higgins, the chief executive of the Olympic Delivery Authority, said that the perimeter fence’s power top, similar to electric cattle fencing, would produce a short, uncomfortable shock but insisted that it would not present any danger to the public or wildlife. It was similar to Network Rail’s fencing and would have warning signs.

Construction of the Olympic stadium is already well under way and 2,500 workers are on site with 4,000 expected by the end of the year and 9,000 at the peak next year. Workers will be subject to biometric screening as they enter the site, vehicles will be screened and security guards will also be hired to protect the venues.

Mr Higgins said: “Given the size of the site and high profile of the Olympic project it is also important to have a perimeter fence that is an effective deterrent while also safe for the local community who live nearby.”

The scale of policing was outlined by Tarique Ghaffur, the Metropolitan Police assistant commissioner, who insisted that the force was working within the £600million budget set by the Government for security. A further £354 million has been put aside for securing the Olympic Park during construction.

But there are signs that the police budget is spiralling higher and Whitehall sources have suggested that the bill, including security in the Olympic Park, could rise to more than £1.4 billion. Speaking at a London conference on security, Mr Ghaffur said that negotiations were still continuing with the Home Office over a new command-and-control centre and the final security blueprint would not be decided till October.

Mr Ghaffur said that extra security forces for the Games would initially be taken from the 32 London boroughs, but an additional 1,000 to 1,500 police officers would be needed from other forces over the 60-day period before and including the Games.

Although final police numbers have not yet been decided he said that 5,500 officers would be needed for peak days such as the marathon and road races, about a sixth of the Metropolitan Police’s total strength.

In addition to using retired officers, Mr Ghaffur said the Met would be using private security staff although many of these are likely to be deployed in the Olympic Park where security will be run by the London Organising Committee of the Olympic Games.

Mr Ghaffur said he was confident that a strong counter-terrorism capability would be in place by 2012 but he was more concerned about the level of “protective services”, including specialist search teams and firearms officers.

“We will need specialist firearms teams from forces all over the country, including the West Midlands and Yorkshire,” he said. He pointed out that firearms officers would need to be trained up over two or three years to gain the necessary skills and this could not be done in just six months.

“We have a number of choices. We can look at our retired officers and see if we can bring them back. We can use people in the private sector and use the special constabulary and bring in more volunteers. In addition we have specialists due to retire before the Olympics and we could retain them for a longer period and renegotiate terms and conditions.”