British police are aiding the hunt for the terrorist plotters behind the Paris atrocities, a senior Scotland Yard officer said.

Metropolitan Police Assistant Commissioner Mark Rowley said officers were offering support to counterparts in France and Belgium and were also attempting to "harvest any information" about the attackers that may be relevant to the UK.

Mark Rowley, the country's top counter-terrorism officer, also said police were using "disruptive" tactics to prosecute extremists for other offences before they begin to plan attacks.

Appearing before MPs on the Home Affairs Select Committee, he said: "In terms of what is going on in France at the moment, clearly after the attack some names have come out to the police in terms of those involved, so it is not surprising that they have got new leads to chase down - new associates and suspects - and they are trying to make arrests and working with colleagues in Belgium.

"We have got officers over there offering support to them and looking to harvest any information that may have relevance to us.

"Clearly the ambition is to prevent attacks."

Setting out the scale of the counter-terror challenge in the UK, he said: "We have been making an arrest a day over the last year or so, which is approaching twice what it would have been three or four years ago.

"I put those in two broad baskets: a third of those arrests are using counter-terrorism powers; we are prosecuting people, whether it's a plot or whether it's having terrorist training or disseminating material.

"Those are the people more advanced in the development of their terrorist intentions.

"The other two-thirds are more disruptive. We are using crime powers, prosecuting them for fraud, sexual offending - anything we can use to disrupt their conduct.

"These are people who are extremists who are generally migrating towards terrorism and rather than waiting to the last minute, anything we can do to disrupt them is important."

He acknowledged that success could not be 100% guaranteed, but added: "Part of the success to date is casting the net broad, going for those involved in plotting but also those involved on the periphery, constantly trying to disrupt them, doing everything we can do to get them on the back foot, which makes it hard for them to find their feet and plan the sort of acts that we saw in Paris."

Mr Rowley confirmed figures used by Prime Minister David Cameron that seven terrorist plots have been foiled in the past year.

The police officer also confirmed there were "several thousand" home-grown terror suspects in the UK.

Mr Rowley said he did not recognise a figure of 300 people on a "watch list" suggested by committee chairman Keith Vaz, insisting that some coverage would be given to all people of concern.

"Out of those thousands of people who are of varying degrees of concern, we are constantly prioritising our operations. Every week there is a prioritisation meeting with the police and the security service together deciding which operations need the most attention.

"Depending how high up operations are on that list depends on how much attention they get. A long way down, we have to pay some attention to them even if we can't have full operational coverage of them."