Insurance companies will be banned from footing the cost of terrorist ransoms, under measures unveiled by Theresa May.

The Home Secretary said the Counter-Terrorism and Security Bill, being introduced to Parliament this week, will make clear it is an offence for firms to reimburse such payments.

The move is part of a package of changes designed to tighten up protections in the UK, amid warnings that the threat of an attack here is growing.

Scotland Yard commissioner Sir Bernard Hogan-Howe has kicked off a nationwide terrorism awareness campaign by disclosing that "four or five" plots have been foiled this year.

He told the BBC's Andrew Marr show that the heightened tempo was putting "pressure" on resources - hinting that he expects the Government to boost funding in the Autumn Statement.

Up and down the country, officers will be briefing more than 6,000 people at 80 venues including schools, universities, airports, shopping centres, cinemas and farms in a bid to engage the public and businesses in preventing attacks.

The terror threat level in the UK was raised from substantial to severe a few months ago against a backdrop of increasing concerns over hundreds of aspiring British jihadis travelling to Iraq and Syria to learn terrorist ''tradecraft''.

Over the weekend it emerged that police are to be handed powers to force internet firms to hand over details that could help identify suspected terrorists and paedophiles.

The Counter-Terrorism Bill will oblige internet service providers (ISPs) to retain information linking Internet Protocol (IP) addresses to individual users.

However, Mrs May has complained that the Liberal Democrats are blocking wider data collection measures - after they declared so-called Snooper's Charter legislation "dead and buried".

Islamic State (IS) linked terrorist groups in Syria and Iraq have been using kidnappings to raise funds - with the UN estimating the tactic has brought in £28 million over the past year.

But the Home Office says there has been an element of "uncertainty" about whether UK-based insurers were prohibited from paying claims made by companies and families who had met ransom demands.

Mrs May, who will address a counter-terrorism event in London later, said: "Our position is clear - ransom payments to terrorists are illegal under UK and international law.

"Agreeing to meet the demands of barbaric groups like Isil would only put many more lives at risk. These measures will ensure the UK remains at the forefront of global efforts to put an end to the practice."

Speaking at the start of the awareness-raising campaign, Metropolitan Police Assistant Commissioner Mark Rowley, national policing lead for counter-terrorism, said: "Police officers and our partners are continuing to work 24 hours a day, seven days a week to protect the UK from a terrorist attack.

"So far this year, we have disrupted several attack plots and made 271 arrests following counter-terrorism investigations but the eyes and ears of law enforcement and other agencies alone cannot combat the threat."

Mr Rowley warned the threat posed by violent extremists has "evolved".

"They are no longer a problem solely stemming from countries like Iraq and Afghanistan, far away in the minds of the public," he said.

"Now, they are home grown, in our communities, radicalised by images and messages they read on social media and prepared to kill for their cause. The tragic murder of Lee Rigby last year was a stark warning to us all about how real and local the threat is."

Mr Rowley has called on the public to be vigilant and report suspicious activity and businesses to check security measures are effective.

Police officers and theatre groups will be speaking to students about the Prevent strategy, which provides help to stop people from being radicalised.

Meanwhile, sniffer dogs will be hunting large amounts of money at ports, airports and railway stations to prevent cash leaving the UK for terrorist purposes.

Other events will follow, including work with farmers to ensure fertilisers - that can be adapted into explosives - are stored securely and charities to advise people about safe ways to donate money.

West Midlands Police assistant chief constable Marcus Beale will address an audience of business representatives in Birmingham this morning.

He will say: "Experience from around the world shows us that terrorists will target busy, crowded places to ensure that attacks have a maximum impact.

"Businesses, particularly those in town and city centres, have an invaluable role to play in preventing potential attacks. Staff working in shops and entertainment centres are often the first people to spot signs that something is wrong."

British Transport Police's (BTP) new deputy chief constable Adrian Hanstock will address rail industry representatives at the National Railway Museum in York.

All week at railway stations across England, Scotland and Wales, BTP officers will be providing counter-terrorism information to passengers and delivering training sessions to rail staff.

In the North West, a briefing on protecting coastal and maritime environments will take place at Brunswick Dock in Liverpool. Assistant Chief Constable Ian Wiggett, the North West lead for counter terrorism, said: "This is not about scaring people, but highlighting that everybody, from law enforcement to businesses, to the general public, has a role to play in keeping the UK safe from terrorism. We encourage people to be vigilant to things that are out of place or suspicious and report it to the police."

IS has posted a series of videos online showing the separate murders of US journalists James Foley and Steven Sotloff, US aid worker Peter Kassig and two British aid workers, David Haines and Alan Henning.

Footage claiming to show Mr Henning's murder appeared on the internet just days after the UK joined US-led air strikes against the terrorists in Iraq.

In addition, an IS fighter with a British accent has appeared unmasked in other films encouraging ''brothers'' in western countries to ''rise up'' and commit acts of terror in their home countries.

America's Federal Bureau of Investigations (FBI) has launched an appeal for the public's help in identifying individuals who have travelled - or are planning to travel - overseas to engage in combat alongside terrorist organisations.