Osborne: Tackling UK terror threat a 'national priority'
Tackling terrorism is "the national priority" and UK security services will get all the resources they need, Chancellor George Osborne has said.
He told the BBC an extra £100m had already been allocated to monitoring Britons going to Syria and Iraq.
It comes as the head of MI5, speaking after the Charlie Hebdo attacks, said three recent UK plots had been stopped.
Meanwhile, the BBC understands two suspects for the attack have been on a UK terror watch list "for some time".
A source told the BBC that brothers Cherif and Said Kouachi - key suspects for Wednesday's deadly attack on the satirical magazine - were on the Home Office Warnings Index, meaning they would have been barred from travelling to Britain.
The Kouachi brothers have been killed following an armed stand-off with police at a warehouse in Dammartin-en-Goele, north of Paris.
In a second incident, anti-terror forces stormed a kosher supermarket in eastern Paris where several hostages were being held by another gunman.
Four hostages were killed but it is not clear whether this was before or after the police assault began. Another four hostages were seriously injured but 15 were freed alive.
The hostage taker - who is believed to have had links to the Charlie Hebdo suspects - was killed.
The Community Security Trust (CST), a Jewish security charity, called on UK police forces to increase patrols in areas of high Jewish populations in London and Manchester, following the crisis in Paris.
A spokesman for Greater Manchester Police said it had increased patrols in Salford and Bury.
It comes as Mr Osborne told BBC Breakfast the UK was facing the threat of a "more complex plot".
"So we have got to be vigilant, we have got to have the resources there," he said.
"My commitment is very clear. This is the national priority. We will put the resources in, whatever the security services need they will get, because they do a heroic job on our behalf."
The financial support for monitoring the "self-starting terrorists" who travel to conflicts overseas after getting "ideas off the internet" was given within the last few weeks, he said.
Security has been increased on the France/UK border following the Paris crisis, in what Home Secretary Theresa May described as a precautionary measure.
The UK terror alert level remains at "severe", meaning a terrorist attack is "highly likely".
Prince Harry has signed a book of condolence at the French embassy in London.
The prince was greeted at the embassy in Knightsbridge, central London, by French ambassador Sylvie Bermann, and wrote the message: "With warmest best wishes".
The book has already been signed by dignitaries including the home secretary and the London Mayor Boris Johnson as well as ambassadors from across the world.
The Queen has sent a message to France's President Francois Hollande in which she expressed her "sincere condolences".
Prime Minister David Cameron tweeted that he would take part in a rally in Paris on Sunday.
The home secretary will also attend a meeting of interior ministers from Europe and the US in Paris on Sunday to discuss the international response to the Charlie Hebdo attack.
'Potentially deadly plots'
Mr Osborne's comments came after the MI5 director general warned that UK security services could not be expected to stop every plot.
In the speech at MI5's headquarters, Andrew Parker warned the UK was facing "more complex and ambitious plots" by extremists.
It comes after a number of anti-terrorism operations in the UK in recent months, including three foiled plots in the last three months.
"Deaths would certainly have resulted otherwise," Mr Parker said.
"But we cannot be complacent. Although we and our partners try our utmost we know that we cannot hope to stop everything."
He said the number of Britons who had travelled to Syria was now believed to be about 600.
He stressed the UK was not facing an "unmanageable crisis", saying "different styles and shapes of terrorism" had been "faced down" for more than 40 years.
But Mr Parker, who was named director general of MI5 in March 2013, revealed security services were aware of a group of al-Qaeda extremists in Syria planning "mass casualty attacks against the West".
He said the number of "crude but potentially deadly plots" MI5 was facing had also increased.
BBC security correspondent Gordon Corera said it was notable that Mr Parker said the UK threat comes from "self-starters inspired by the group calling itself Islamic State" as well as groups linked to al-Qaeda in Syria.
Conservative Sir Malcolm Rifkind, chairman of the Commons Intelligence and Security Committee, said the Paris attacks had given "added weight" to the case for intelligence services to get stronger powers to intercept communications and it was becoming "increasingly difficult" to access vital evidence.
Sir Peter Fahy, vice-president of the Association of Chief Police Officers, told BBC Breakfast: "In the past, it was just about big plots coming in from the outside.
"Now we're just as concerned about individuals in this country being rapidly brainwashed on the internet and suddenly deciding to perform some chaotic attack. So we've got to be vigilant to both."