May and her Home Secretary Amber Rudd were reeling from attacks from across the political spectrum over the disgraceful treatment of the so-called Windrush generation – Caribbean migrants who arrived in the UK to help in the post-war reconstruction effort from the late 1940s onwards.
In their wisdom, Home Office officials decided to concentrate their resources on chasing these migrants, who entered the UK legally and have led blameless lives for decades, working, paying taxes and raising families.
Some of them, through no fault of their own, entered the UK on their parents’ passports and have never held any official documentation showing their right of residence here.
These are the same Home Office officials, let’s never forget, who are happy to roll out the red carpet for returning jihadis from Syria and who allow vile hate preachers to enter the UK to spread their poison.
Not for the first time I found myself asking – where on earth do they find these people?
Any fair-minded person could see that government policy was indefensible and May and Rudd, as former and current Home Secretaries, were very much in the firing line.
So, at the big set-piece Prime Minister’s Question Time in the Commons this week, Corbyn was presented with a yawning, empty net with the ball nicely placed virtually on the goal line.
All he had to do was to tap it home, but somehow, incredibly, he managed to scoop it high over the bar and hoof it into row W of the stands.
Corbyn’s mistake, as is often the case, is that he failed to do his homework properly.
He should have heeded the timeless advice of the cynical old Commons veterans – never ask a question unless you are absolutely certain you already know the answer.
Corbyn homed in on the issue of the landing cards of Caribbean migrants, which might help prove their date of arrival, and which inexplicably have now apparently been destroyed.
“Did the Prime Minister – the then Home Secretary – sign off that decision?” he asked.
The sides of Mrs May’s mouth lifted a little and for a fraction of a second a look of barely suppressed triumph flickered across her face. It was a gesture that said: “I’ve got him now!”
She rose to her feet and delivered the killer blow: “No, the decision to destroy the landing cards was taken in 2009 under a Labour government.”
Oomph! Direct hit! The Conservative benches went nuts, while their Labour counterparts suddenly found fascinating things to look at on their mobile phones.
All the while Corbyn gasped and wheezed like steam rising from a busted radiator after a particularly horrible car crash.
The poor man! He simply does not posses a sharp enough intellect to think on his feet and come up with a reasonable retort on occasions like these.
So what started as a bad day for May, turned into a disastrous day for Corbyn.
But, as entertaining the gladiatorial battles in the Commons can be, it doesn’t get the Government or the Home Office off the hook.
The substance of the charge remains – that Government officials persecuted entirely blameless, law-abiding people who are here legally, while all the while throwing open our borders to all kinds of terrorists and benefits bandits from across the globe.
A grandmother who left Barbados for the UK at six years of age and has lived all her life here since, is as British as you or me, and we should be grateful to the “Windrush generation” for the fantastic contribution they have made to British life.
We certainly shouldn’t be hounding people, many of them elderly, over non-existent immigration transgressions.
And if heads roll as a result of this debacle – so be it, although I will believe it when I see it.
I admit to a soft spot for Mrs May, simply because of her undoubted courage under fire. But, as for the over-promoted Mrs Rudd, I can’t see she will be much of a loss.
True to form she is now busily blaming everyone else, including officials she manages, while dodging any personal responsibility.
She is the boss and she should carry the can.