THE pendulum has a tendency to swing very fast in British politics.

It was the start of the week when Boris Johnson had to don his constitutional helmet to protect himself from the barrage of criticism that came his way after his infamous “devolution north of the border has been a disaster” gaffe.

But within 24 hours Keir Starmer was attaching his body armour to deflect the flak from Labour’s left wing over his decision to turf his predecessor Jeremy Corbyn out of the Parliamentary Labour Party.

Bad blood is once again percolating to the surface of HM Opposition, a situation that is likely to hinder Sir Keir for some time to come given the characters involved on both sides.

Anneliese Dodds, the Shadow Chancellor, popped up on the airwaves to point out how the Equalities and Human Rights Commission, which published the damning report on anti-Semitism within Labour ranks, had found the party’s disciplinary process to be not fit for purpose and should be replaced by an independent system.

“It’s a matter of huge regret and shame to my party that it found we were wanting,” declared the Scot. “We have to sort out that system. It cannot remain as a politicised system. Keir Starmer has committed to altering it and…we are now under a statutory duty[to do so].”

Which bodes one question: why was Mr Corbyn’s case fast-tracked after just 19 days to have his case determined by a politicised system? Surely, this was just asking for trouble.

Or, as some suspect, was the process all about making an example of the former leader by the current one; given the most important audience is not Labour members but voters.

Of course, the opponents of Mr Corbyn decried the fact that, after his suspension, he had been allowed back into the party; the system was politicised, they cried.

But for the supporters of Mr Corbyn when Sir Keir refused to return the party whip at Westminster to him, they cried foul, saying this was politicised.

To make matters worse, it was suggested that a behind-closed-doors deal had been hatched and then welched on.

Mr Corbyn was suspended because he had not taken the commission’s report at face value and insisted the scale of anti-Semitism had been “overstated,” only for him, post his suspension, to issue a “clarification”, saying concerns had not been exaggerated.

The suggestion was that the change of tack would see the 71-year-old London MP return not only to the party but also to the Labour benches in the Commons, where he has sat for 37 years.

Len McCluskey, General Secretary of the Unite union, Labour’s biggest donor, and a key ally of Mr Corbyn, together with John McDonnell, the former Shadow Chancellor and another chum of Jeremy, had supposedly tried to broker an agreement with David Evans, Labour’s General Secretary, and Simon Fletcher, Sir Keir’s campaign adviser.

But when the Labour leader saw the level of anger from Jewish campaigners about the return to the party fold of the head leftwinger, one suggestion is that he took fright and kicked Mr Corbyn out of the PLP.

Yet, Sir Keir’s team was quick to insist there was no deal; just a hope from the Corbynites that their man would be restored as a Labour MP.

Some of the language used against the party leader – “vengeful,” “vindictive,” and a “blatant political attack on the Left,”- underscores the rift once again opening up between Labour’s left wing and the centrists or, as they will no doubt become called in time, the Blairites.

Momentum, the pro-Corbyn campaign, is on the warpath while around 30 Labour MPs are demanding Jeremy’s reinstatement as a Labour MP.

Yet for Sir Keir, in this and everything else, his prime motivation is simple: winning power.

Losing five general elections in a row and being out of office for what would be at least 19 years if Labour lost the 2024 poll would be unconscionable.

The party leader made clear on the back of the commission’s report that no one should downplay or refuse to accept the level of anti-Semitism that had been allowed to fester during Mr Corbyn’s time at the top. Sir Keir’s allies insist there was “no reconciliation, no sense of regret, no apology,” from the 71-year-old London MP. Jeremy had to go.

Defending his action, Sir Keir declared: “I know that I will be judged on my actions, not my words.”

One senior ally noted: “What the public will see in all this is Keir acting as a true leader.”

The issue of the whip being withheld from Mr Corbyn is now set to be discussed at the next virtual meeting of the PLP on Monday.

One senior figure said there might be a move by some MPs to seek the ex-leader’s reinstatement to the parliamentary party but they would not succeed. “The Left is very weak now; they have a social media presence but that’s it.”

After months of bad headlines over pandemic U-turns, a UKwide YouGov poll has put the Tories back in the lead on 38 points, just one ahead of Labour. Half of the public backed the decision not to reinstate Mr Corbyn to the PLP yet only 38% of Labour voters did.

That perhaps is a good return for the man-who-would-be-prime-minister but it shows the scale of the internal strife he has to overcome. There will be an awful lot of pendulum swings to go before Sir Keir has any chance of entering No 10.