Tonight is the last of ITV’s remarkable four-part drama about the Post Office Horizon scandal, which is one of the greatest miscarriages of justice ever in this country.

Between 1999 and 2015, more than 700 sub-post masters and mistresses were prosecuted for theft and fraud due to evidence alone from a faulty computer system. They had their reputations ruined and their lives and livelihoods destroyed. Hundreds were imprisoned for things they had not done, and probably four committed suicide.

The programme is a hard watch because we see ordinary, innocent people being crushed to the point of extinction by an overbearing system that was desperate to protect itself.

It is astonishing that this should have happened so recently in our country, and that the perpetrator – the Post Office – should be an arm of government. It is astonishing that the Government is only slowly paying compensation to the victims of the scandal, even though some are now dying due to old age.

And it is astonishing that no one from the Post Office or the computer suppliers Fujitsu has ever been held accountable, even though they deployed ruthless tactics to smash the little people.

The postal workers were the victims of our “computer says no” culture, where what a computer says is unquestioningly accepted. They were the victims of our society where big business, and big government, is too far removed from the grassroots people it is supposed to serve.

The cases were prosecuted using “evidence” from a computer system that the extravagantly-paid big bosses said was infallible but which the humans on the ground, trying to scratch a living, knew had flaws.

The ITV drama has made viewers feel incensed by the injustice and then so vulnerable – it could have been any one of us on the receiving end of an almighty system. As we enter the era of artificial intelligence where computers are getting mightier still, this drama must act as a caution that IT cannot be allowed to crush humanity.