Boris Johnson likes to think of himself as a “big picture” guy. When it comes to governing London, exiting the European Union and running his own leadership campaign, he leaves the details to others.

Sadly this approach to the job has left the big picture looking pretty bleak for one British mother, Nazanin Zaghari-Ratcliffe. Imprisoned on false charges of espionage while visiting her family in Iran, the Evening Standard has championed the case of this Londoner and brought it to public attention.

Now the Foreign Secretary has potentially prolonged her incarceration by blurting out before a parliamentary committee that he thought she had been in Tehran training journalists.

He got the facts wrong. Ms Zaghari-Ratcliffe was on holiday — and that is her key defence. But the Iranian authorities have seized on Mr Johnson’s remarks as evidence to support their case that she was spreading “propaganda”.

Mr Johnson made a stupid, careless mistake because he wasn’t on top of the detail — a mistake that her family believes could have “dangerous” consequences.

Rather than quickly apologise and correct his error, he got the Foreign Office to issue a ridiculous statement that he was, in a convoluted way, in fact trying to help.

Spare us, please. We imagine that consular cases are a frustration for our Foreign Secretary. He must feel that they get in the way of the “Great Game”.

But as a fan of classical allusions, Mr Johnson will remember what that impressive Foreign Secretary Lord Palmerston promised more than 150 years ago: just as an ancient Roman would always have protection because they could say “civis Romanus sum” (“I am a citizen of Rome”), so our own citizens were entitled to the “watchful eye” and “strong arm” of Britain to protect them from “injustice and wrong”.

We don’t have the legions stationed around the world any more always to respond with force. What we do have are intelligent, persistent diplomacy and a global voice. We should use it.

The Foreign Secretary should come to Parliament, retract his mistake and dramatically step up his efforts to free Ms Zaghari-Ratcliffe, citizen of Britain.

Rail: a triple whammy

Tomorrow commuters face lengthy delays on three key rail networks as RMT workers stage a 48-hour walkout.

Passengers on Southern routes have become grimly used to the misery caused by strikes, having endured numerous stoppages over the past 18 months. Now they will be joined in their dismay by travellers using South Western and Greater Anglia services, which are also affected.

In an open letter to the Evening Standard, Transport Secretary Chris Grayling expresses his frustration at the continuing dispute.

Unions claim that they oppose the move to driver-operated doors for safety reasons — but that is disingenuous since many services already work perfectly well in this way. Nor will there be fewer jobs.

Indeed, Mr Grayling makes the point that, on an increasingly crowded railway, there are likely to be more staff in the future, not fewer, though some of them will be working on platforms rather than in carriages.

The row over driver-only operation has become emblematic for union chiefs who appear desperate for a showdown with the Government.

Yet it is ordinary people, paying over the odds for their season tickets, who suffer from these unnecessary strikes — and they have already suffered more than enough.