Politicians will always be vulnerable to sudden violence

Her attacker reportedly shouted a slogan, “Britain first”, before killing Ms Cox.

Although such a remark, which is also the name of a far-right group, suggests a link to the EU referendum, the Remain and Leave camps have come together in shock.

The referendum campaign has been rightly suspended.

After a period of collective mourning, the campaign will resume, as it should, and democracy will grind on.

All individuals are vulnerable to being targeted at any moment by a lone attacker with a knife and there is very little society can do to stop it. Politicians have a profile and so are more likely than most people to attract unwelcome attention.

This has all the hallmarks of a crazed assault. Two other MPs in England have narrowly escaped death in similar attacks.

Stephen Timms, also a Labour MP, was stabbed in 2010 by a woman who claimed she was taking revenge for his support in the war in Iraq.

In 2000, the Liberal Democrat MP Nigel Jones was injured and his assistant was killed when a man wielding a samurai sword attacked them. The attacker later claimed that Mr Jones had not done enough to help him with a problem. Psychiatrists assessed the man as mentally ill and he was put in a secure unit.

Attacks on politicians in which the attacker is deranged are tragic for all concerned.

Attacks on politicians by sane but fanatical political opponents are, however, despicable.

In Northern Ireland we have had several of the latter, including the brutal terrorist murders of the SDLP’s Senator Paddy Wilson and the UUP’s Robert Bradford and Edgar Graham.

Politicians often come in for bitter criticism but the fact that so many of them remain in public life despite the opprobrium they can receive is something for which we should be thankful because such participation makes democracy possible.