Prime Minister John Howard is warning the public not to be under the illusion Australia is immune to a terrorist attack.

Although there was no specific intelligence to suggest an attack in Australia, Mr Howard said the nation was as vulnerable to terrorists as any other country.

London yesterday became the latest city to feel the chilling effects of terrorism when a series of four bombs crippled the transport network and killed at least 37 people.
 

The blasts, which tore through three commuter trains and a double-decker bus during the morning rush hour, also injured about 700, including nine Australians.

"I have never hidden or concealed my view that this country could experience a very serious terrorist attack," Mr Howard told reporters after meeting high-level intelligence experts.

Both the government and Labor stood firm that the British atrocity would not influence the decision on whether to boost Australia's troop numbers in Afghanistan.

Unconfirmed reports suggest the attack was by an al-Qaeda linked group in retaliation for Britain's role in the war against terrorism in Iraq and Afghanistan.

"If anybody imagines that these attacks will intimidate the government in any way, they would be wrong, that does not mean that we have decided to make a fresh commitment to Afghanistan," Mr Howard said.

Australia is maintaining its medium terrorism alert level but security experts are urging authorities to reassess the threat to the nation's transport network.

Myles Newlove, managing director of risk management group Aurora Intelligence, believes Australia's public transport systems are almost impossible to protetc.

"(This attack shows) there is a shift in tactics by terrorist groups to exploit the vulnerabilities of a public transport system," he said.

"We've improved our security measures elsewhere but it still comes back to the same thing - our public transport is one of the most open systems I have seen in the world, so that is a prime target for terrorist attack."

Aldo Borgu, from the Australian Strategic Policy Institute, said authorities had done considerable work on maritime and airport security and now was the time to look at land transport networks.

"It's probably about time we started looking at land security and particularly trains, bus services, ferries and the like operating in Australia," he said.

Authorities in Melbourne and Sydney have stepped up surveillance on the extensive rail networks in Australia's two biggest cities.

Melbourne, which will host next year's Commonwealth Games, also raised the prospect of increasing its security budget to deal with the spectre of terrorism.

Victoria's Commonwealth Games Minister Justin Madden said security for the March event was constantly under review, stressing there was no cap on spending.

Federal and state governments are spending more than $150 million on security and counter-terrorism measures for the Games.

Mr Howard announced Australia would send a team of six experts to help British authorities with their investigations, including a transport official who could bring back advice on how to deal with such situations.

The team will comprise three federal, one Victorian and one NSW police officers, as well as an officer from the Department of Transport and Regional Services.

Mr Howard said sending the transport officer would help Australia deal with a similar situation if it ever had to cope with an attack.

New British High Commissioner Helen Liddell welcomed the police assistance.

AAP