They are being lined up as a second line of defence against those planning atrocities against the UK beyond the traditional security and emergency services, it has emerged. The move forms part of the Home Office's updated counter-terrorism strategy, to be published tomorrow, which will repeat warnings that the greatest threat comes from groups linked to al Qaeda. The move also reflects concerns following recent attacks on hotels in the Indian city of Mumbai and comes as an unprecedented security operation is being mounted in London for the G20 summit next month.

Last Saturday, The Daily Telegraph disclosed that senior counter-terrorism officials rated the threat of a terrorist attack as 'highly likely'.

But the Conservatives said the Government was still not doing enough to tackle the threat from those within the UK.

Prime Minister Gordon Brown said the public must remain "vigilant at all times" adding: "Tens of thousands of men and women throughout Britain – from security guards to store managers – have now been trained and equipped to deal with an incident and know what to watch for as people go about their daily business in crowded places such as stations, airports, shopping centres and sports grounds."

Home Secretary Jacqui Smith said the revised terror measures – known as Contest Two – would provide "a complete strategy to address counter-terror".

"What we're completely clear about is that if we're going to address the threat from terrorism, we need to do that alongside the 60,000 people that we're now training up to respond to a terrorist threat, in everywhere from our shopping centres to our hotels. We need to do it alongside the 3,000 police officers now working on counterterror... and we need to do it with international partners.

"This no longer is something you can do behind closed doors and in secret."

Tomorrow's document will reflect security services' judgment that the most serious terror threat to the UK continues to come from international groups linked to or influenced by Osama bin Laden's al Qaeda network.

Experts have spent a year preparing the document to take into account lessons learnt from recent terror outrages such as the attacks on hotels in Mumbai last year.

But Shadow Home Secretary Chris Grayling said: "The horrific recent events in Mumbai have highlighted the need for a different strategy in counter-terrorism – and the whole community needs to be involved in tackling the danger.

"No part of the UK is free from threat and we know that terrorists want soft targets.

"My big concern is that the Government is still not doing enough to tackle the problem of individuals and groups in the UK who are fostering the hatred and extremism that lies behind the terrorist threat."