Cameron, Abbott and Obama
Western leaders, including Abbott, Cameron and Obama, have to weigh up how best to deal with small scale terrorismReuters

The unfolding hostage siege in Sydney is part of a growing trend of "small scale, lone actor" terrorism across the Western world, according to The Henry Jackson Society.

The thinktank told IBTimes UK that the terrorist threat is "always there" in the West and governments are "having to weigh up how best to deal with it".

But the organisation warned that there is only "a limited amount" that any state can do about a lone actor holding up a "low-risk" building such as a cafe.

"What we are seeing is the rise of small scale, lone actor terrorism that relies on guns and knives rather than complex bomb-making," said Robin Simcox, a research fellow at The Henry Jackson Society.

"The methods used in recent months in London, Paris, Ottawa and now Sydney are the blueprint that others will follow.

"This is a shift that was taking place even prior to this year, when Is (Islamic State) explicitly encouraged such attacks."

The comments come as at least one gun man has taken customers and staff hostage in a Lindt cafe in Martin Place, Sydney – one of the city's main business areas.

Police have confirmed that so far five hostages have been released and media reports have claimed that around 15 hostages are left in the building.

A major police operation continues and the area surrounding the café has been cordoned off.

The UK Prime Minister said he is "deeply concerned" about situation as the stand-off continues.

"I was briefed overnight on the siege in Sydney. It's deeply concerning and my thoughts are with all those caught up in it," David Cameron said.

Simcox told IBTimes UK that the British authorities are "well placed" to deal with a similar threat.

"The UK has being preparing its responses for various kinds of terrorist attack for several years and are well placed to deal with this kind of threat," Simcox said.

He also said he does not expect the government to introduce new laws or measures following the Sydney siege since the Home Secretary, Theresa May, recently unveiled a raft of new counter-terrorism measures.