A man who posted a death threat to a British lawmaker was on Friday jailed for a year, the public prosecutor announced, as it published a safety guide for general election candidates.

EU and UK flags are seen outside the Houses of Parliament, in front of a statue of Winston Churchill, in London, Britain on Jan. 15. 2019. The British parliament on Tuesday rejected overwhelmingly the Brexit deal, further complicating the country's historic exit from the European Union (EU). (Xinhua/Tim Ireland)

Alden Bryce Barlow was convicted in Sheffield, northern England, after admitting to sending the letter to Anna Soubry, which read "Cox was the first, you are the next." 

Labour MP Jo Cox was shot dead by a neo-Nazi during the 2016 Brexit referendum campaign.

The letter, sent to Soubry's constituency office in Nottingham, central England, also described Soubry, who has fought to overturn Brexit, as "treacherous" and "worthless."

Prosecutor Gerry Wareham said he hoped the sentence "comforts Ms Soubry and colleagues and deters anyone who would consider such despicable acts against a parliamentarian or a candidate."

Drawn up with police and the Electoral Commission, the Crown Prosecution Service's advice urges candidates not to canvass alone and "take active" steps to protect themselves with tensions already running high ahead of the December 12 vote.

"Abuse or intimidation of candidates in elections has serious implications for individuals and for our democracy," said National Police Chiefs Council chairman Martin Hewitt.

"Strong and varied views are the mark of a healthy democracy but these should not cross the line into criminal abuse, harassment or disorder." 

Candidates are advised to "keep records of any intimidating behavior or abuse" and conduct an "online personal health check" to ensure sensitive personal information is not widely available.

The political atmosphere has deteriorated sharply in Britain since the 2016 Brexit referendum campaign and tensions are set to reach fever pitch ahead of the key vote.

Online death threats and harassment on the streets are now common occurrences for lawmakers. Several female MPs have announced they will not stand for re-election because of the levels of abuse.

A pro-Brexit activist received a suspended jail sentence in July for shouting "Nazi" and "traitor" at Soubry, who was a member of Prime Minister Boris Johnson's ruling Conservative Party before becoming an independent.