The government’s adviser on political violence has written to the home secretary asking to investigate the intimidation of candidates during the general election.

Lord Walney is suggesting there could have been a “concerted campaign by extremists”.

He is urging Yvette Cooper and Security Minister Dan Jarvis to commission a short inquiry to find out if groups in different constituencies were working together and to document what he calls the “dark underbelly” of abuse.

The Home Office said it takes reports of intimidation, harassment and abuse “extremely seriously”, adding that officials are contacting affected individuals.

In the letter, seen by the BBC, Lord Walney said evidence from the last couple of months points to a “concerted campaign by extremists to create a hostile atmosphere for MPs within their constituencies to compel them to cave into political demands”.

He writes the “conduct of the election campaign in many communities has underlined the gravity of the threat to our democracy” from the abuse and intimidation of politicians, local and national.

Lord Walney said: “I am increasingly concerned about the scale of intimidation against candidates in the general election.

“I believe there is now a need for a focused piece of work on the scale and drivers of this intimidation so that it cannot continue to mar our democratic processes and put candidates at risk.”

On the eve of the election, a review from Lord Walney called on ministers to update and extend the ways in which politicians and Parliament are protected.

After the events of the campaign, he suggests the new government might have to go further.

His concerns follow comments from the Speaker Sir Lindsay Hoyle, who told the BBC: “if there is something that keeps me awake at night, it is the safety of MPs“.

During the election campaign, candidates reported a hammer attack on their office, masked men interrupting a community meeting, tyres being slashed and MPs being filmed and followed.

Sir Lindsay said he had “never seen anything as bad” as the current level of intimidation.

Labour lost votes to pro-Palestinian candidates, angry with the party’s position on the Israel-Gaza conflict.

Reform UK leader Nigel Farage had a milkshake and other objects thrown at him during the campaign.

Several MPs reported harassment and attempted intimidation of them and their supporters.

In response to news of Lord Walney’s letter a Home Office spokesperson said: “Political intimidation and abuse should have no place in our society.

“We take reports of intimidation, harassment and abuse extremely seriously and are following up with individual MPs and candidates”.