National Union of Students launch 'decapitation' strategy aimed at ousting Nick Clegg and other top Liberal Democrats in protest at the party's U-turn on tuition fees

The National Union of Students will launch a "decapitation" strategy aimed at ousting Nick Clegg and other top Liberal Democrats from parliament in protest at the party's U-turn on student fees.

The move aims to build on anger about coalition policies – which spilled over into violence on Wednesday – in Lib Dem-held constituencies with large student populations.

The key targets will be Clegg in Sheffield Hallam, Simon Wright in Norwich South, Stephen Williams in Bristol West and Don Foster in Bath.

Aaron Porter, president of the NUS, said the campaign would aim to force out Lib Dems who break their pre-election pledge to oppose any rise in tuition fees. The move has echoes of the Lib Dems' own "decapitation strategy" in 2005, when the party threw resources into efforts to oust leading Tories with narrow majorities, including Michael Howard and Theresa May.

Porter said the NUS will make use of a coalition idea for holding MPs to account that was championed by Clegg himself. The "right to recall" initiative, which has yet to became law, proposes that a byelection can be called if an MP is judged guilty of serious wrongdoing and 10% of constituents want him or her removed.

More likely is that the NUS could mobilise support against selected MPs ahead of the next election. Extra efforts will be made in the four target seats – with 1,000 students taking to the streets of Sheffield in an attempt to get 10% of Clegg's constituency to sign a petition.

The Lib Dem leader, who held Sheffield Hallam with a majority of 15,284 at the May election, has around 10,000 students in his constituency. Others could be more vulnerable, such as Wright, who beat Charles Clarke in Norwich South by just 310 votes. Porter said: "It will serve to undermine the wafer-thin mandate this government has on university cuts and debt."

Students will not target MPs who have promised to vote against the policy to raise fees to as much as £9,000, such as Tim Farron, who has just been voted Lib Dem president. Farron opposes the rise but insists the Lib Dems had made it a fairer package than it would have been under either Conservative or Labour.

Evan Harris, the former Lib Dem MP who topped the elections for the party's federal executive, attacked the campaign as a "partisan stunt". He pointed out that manifesto promises could only be fulfilled if a party won a majority and said the NUS never suggested voting against, "let alone recalling", Labour MPs who broke election pledges on top-up fees.

However, Caroline Dowd, Sheffield Hallam University's student union president, said her members were livid. "We could not get [Clegg] out of our union before the general election. He came and spoke about how MPs should not make promises and then break them, about how fees were wrong."

She said there were 1,000 students in Sheffield prepared to take to the streets to gather names for a petition and there would be a protest outside Clegg's constituency office on Thursday.

Clegg's problems mounted as the Guardian revealed secret documents showing that he and other senior Lib Dems were preparing two months before the election to drop their promise on fees in the event of a coalition..

John Denham, the shadow business, innovation and skills secretary, said Clegg had no "credibility" left on the issue. "This week he said he should have been more careful before promising he would vote against fee increases, but now we know he was planning to drop his policy long before he made this promise."

A Lib Dem spokesman said: "What we have achieved is a system that is fairer than the one that exists now which means the poorest 25% of graduates will pay less, and those who go on to earn more pay more."

The controversy comes as police arrested a 57th person in connection with last week's student march through London, which ended in violent scenes. As police face continued criticism for failing to control the march, the Observer has learned that defence firms are working closely with UK armed forces and contemplating a "militarisation" strategy to counter the threat of civil disorder.

The trade group representing the military and security industry says firms are in negotiation with senior officers over possible orders for armoured vehicles, body scanners and better surveillance equipment.

The move coincides with government-backed attempts to introduce the use of unmanned spy drones throughout UK airspace, facilitating an expansion of covert surveillance that could provide intelligence on future demonstrations.

Derek Marshall, of the trade body Aerospace, Defence and Security (ADS), said that such drones could eventually replace police helicopters.

He added that military manufacturers had discussed police procurement policies with the government, as forces look to counter an identified threat of civil disobedience from political extremists.

Meanwhile police sources say they have detected an increase in the criminal intentions of political extremists and are monitoring "extreme leftwing activity" in light of last week's student protest.

The office of the National Co-ordinator for Domestic Extremism (NCDE) said it was feeding information to Scotland Yard's National Public Order Intelligence Unit, which holds a database of protest groups. NCDE, which in turn works closely with the Confidential Intelligence Unit that monitors political groups throughout the UK, said it had already recorded a rise in politically motivated disorder.

An NCDE insider said: "Over the past year there has been an increase in the criminal activity committed by such individuals but this is committed by a very small minority".

An internal Metropolitan police report is expected to be completed this week into why senior officers failed to anticipate the violence during last Wednesday's student demonstration.