Rishi Sunak does not like disagreeing with Boris Johnson, the man he calls “the boss”. The chancellor also wants to be seen as a prudent guardian of the public finances. It is not exaggerating to say that he will have to choose between the two on the issue of uprating pensions next year.

Number 10 has made its position clear. It wants to press ahead with the “triple lock” on pensions, saying repeatedly this week that ministers, “made a commitment on triple lock and plan to stick to that commitment”.

The prime minister’s position sits awkwardly with a statement from the chancellor, also this week, that he was committed “to get the public finances on a sustainable footing” and the government would take “the difficult but necessary steps . . . to keep debt under control”.

Normally, these two positions would be easy to reconcile. The government has a manifesto commitment to stick with the triple lock and uprating pensions by the highest of average earnings growth, the rise in consumer prices or 2.5 per cent does not break the bank. Not so in 2021.

Sunak’s problem is that the triple lock this year is an absurdity. When the decision is due in the autumn, there is no doubt that the highest of the three indicators will be earnings growth. It is currently showing an annual rise of 5.6 per cent and is on course to reach around 8 per cent in the three months to July, the relevant period for pension uprating.

The exact figure is uncertain. When it is published in September, earnings growth might be 7 per cent or it might be as high as 9 per cent, but there is no doubt that the figure will be both high and will bear little relation to actual pay increases.

The statistic is boosted artificially because the annual comparison is made with the first wave of the coronavirus pandemic last year, when millions were furloughed and receiving less than their normal pay.

A further problem is caused by the pandemic hitting part-time and low-wage work, thereby boosting the apparent level of average earnings. Instead of the 5.6 per cent headline rate, the Office for National Statistics estimates that underlying wage growth is around 3 per cent.

With £85bn of pensions affected by the decision, the chancellor is staring at an annual bill of around £4bn a year to stick to the pledge. Sunak has so far sat on the fence, saying that nothing should be decided until the real uprating parameters are known in the autumn. This is understandable prevarication, but everyone knows the choice is coming and a decisive chancellor would bite the bullet.

For a chancellor to accept an additional £4bn a year of public spending purely as a result of statistical anomalies would show weakness. That is about the same cost as Sunak has saved by cutting overseas aid to the poorest countries.

Sticking to the triple lock would amount to the UK government telling poor countries that it has diverted aid money to its pensioners purely because a rich country’s statistical office cannot produce a reliable estimate of earnings growth.

But the situation is more serious because, as the name suggests, a feature of the triple lock is that large and anomalous increases are locked in. Earnings growth was negative last year, but this was not reflected in the 2021 uprating and measured earnings growth might be very low again in 2022 as the statistic reverts to normal patterns, but pensions will again rise by at least the minimum 2.5 per cent.

No prudent chancellor would allow their priorities for public spending or their ability to put the public finances on a sustainable footing to be buffeted by the vagaries of a highly distorted statistic. This is Sunak’s moment to show what sort of chancellor he is.