It is inevitable that the tone of the referendum campaign will change. The cheerful slugfest of accusation and name-calling would seem grotesque after last week’s terrible event. But what will not – must not – be allowed to change is the substance of the argument. A hideous and pointless murder must not be elevated to the stature of a political statement. It must not, in effect, be given a meaningfulness that it does not deserve. It must be made absolutely clear by everyone of good conscience that acts of violence by unstable individuals have nothing to do with political discourse and cannot rewrite its rules.

According to all the available testimony – including the official police statement – this was an isolated incident with no connection to any wider organised forces. The accused man had a history of mental illness. His alleged attraction to far-Right extremism has been featured widely in the coverage of the crime.

So let’s state this categorically: the alleged murderer Thomas Mair is no more representative of voters’ concerns about uncontrolled immigration than the murderers of Fusilier Lee Rigby were representative of the British Muslim community.