Peter Williams, 66, contacted Mrs Allen’s office numerous times with dozens of emails over a two-year period following her election in May 2015.

He became particularly irate after July last year when he learned that he wouldn’t receive a full state pension of £137-a-week when he turned 65. 

This is because he receives a payment from the Ministry of Defence (MoD) which stems from injuries he sustained from his nine years’ service as an aircraft technician. 

He claims he receives £22 a week pension payment from the Department for Work and Pensions (DWP) in addition to his payment from the MOD.

In February the former postman turned to Mrs Allen, his local MP for South Cambridgeshire, for help getting his full state pension, Huntingdon Law Courts heard.

When he thought her office was making a lack of progress with the matter he sent them two “threatening” emails in March.

One, sent on March 8, said: “Put it this way, if I walk into your office and hit you over the head with a sledgehammer and caused you to suffer injury and the next week you are 65, what are you entitled to?”

On March 27 he sent another email which said: “If I stepped into your office and injured you today and you are 65 next week what might you receive if you remain alive?”

The Hardwick office, in Cambridgeshire, was run by office manager Nicola Wade and case worker Nicola Gillan – who worked one day a week.

They both monitored Mrs Allen’s parliamentary email account, where Williams admitted sending the emails, all addressed to the MP.

Mrs Wade had worked for Mrs Allen since 2015 rising from a senior parliamentary assistant to the office manager. 

She said the “language” of the emails changed when they started helping him with issues he was having with his pension.

After receiving the first email, she said: “It was worrying because this was around the time that [Labour MP] Jo Cox murdered. Up until then I thought I just worked in an office.

“But then I realised I work for an MP and that puts us in a certain amount of danger. That is why we sent it to the policeman to see if it’s something we should be worried about.”

The day after the second email was sent Williams phoned the office and spoke to Mrs Wade.

She said: “It was about his issue with the DWP but he referred to the stabbing in parliament the week before where the policeman [Keith Palmer] had died [in the Westminster Bridge attack]. That really worried me.

“He said that he had never killed anyone but that it was the policeman’s fault that he got stabbed because he hadn’t worn a vest. 

"He said he wouldn’t kill anyone like that. He said he had never killed anyone and then he said 'if I came into your office and attacked you with a sledgehammer you would want compensation'.

“He was insisting that Heidi spoke to the Secretary of State about his pension. He then said 'fine I’ll take matters into my own hands' and hung up.”

She added: “I had a meltdown at that point. I was very, very scared. I was in the office on my own that day and I was very scared. He was angry.”

He later rang the Westminster office where he left the female worker there “shaken”.

Mrs Allen, an outspoken Remain MP, then appeared in the witness box. She said she had grown used to receiving “repetitive” emails from Williams over a two year period on minor issues.

She reacted by automatically deleting them. She initially deleted the March 8 email but after half an hour or so went into her junk folder. She then decided to forward it on to Chief Inspector James Sutherland from Herts Police.

She said: “I thought this is not acceptable. This is threatening and I have to do something about it.

“At the time I had no male employers. They (my female staff) are often alone. I was uncomfortable with the fact that he might come to the office.

“I suppose the threat of that, if that’s the right word, is the talk about coming into the office.

“You are very exposed as an MP. I have surgeries all over my constituency. 

"Does that mean that you should find yourself always looking over your shoulder when you are out and about in your constituency? To me that’s not fair.”

Saying that she would rather not look at Williams she said: “[Det Insp] James [Sutherland] advised me to have a couple of male counsellors at my surgeries. I often have my husband with me. The first surgery after they sent a PCSO.”

She said the “repetitive” nature of the contact would be called “trolling” in social media.

Mrs Gillan said: “There is still an inherent sense of threat to me as the reader.

“We felt concerned because he had used the statement “if you remain alive”.

When questioned as to why they never told Williams to stop sending emails she said: “Because his actions were becoming more unpredictable we didn’t know what sending an email (asking him to stop) was going to do.”

On March 30 four policemen went to Williams' home in Great Shelford, Cambridgeshire, to arrest him. 

When asked to go to the police station he declined and said he would attend “voluntarily” at a later date because he was busy.

As they tried to handcuff him he pushed PC Louis Newton, causing him to stumble back.

Williams was then pepper sprayed while another used a baton to bring him to the ground.

He only stopped resisting when PC Newton threatened to use a taser. The arrest left PC Newton with minor injuries to his left hand and arm.

Williams was later charged with harassment without violence and resisting arrest.

He denied both claiming that he didn’t harass Mrs Allen or her staff because he was only talking about hypothetical “scenarios”.

The pensioner also denied resisting arrest by claiming it was unlawful.

Deputy district judge Paul Booty found him guilty of both offences and ordered him to pay £700 in fines and costs.

He also gave him a 12-month restraining order against contacting Mrs Allen and her staff.

Sentencing, he said: "I think it is absolutely plain that sending the messages that you did to lone female workers, a reasonable person could see that it would amount to harassment, and for that I find you guilty. 

"You are a man of good character and that of course has its own bearing on not only this case but on the evidence you provided formally today.”