When Jonny Bairstow was promoted to be England’s long-term No 5 last week, he was not only attempting to shore up the team’s rickety top-order batting, he was also attempting to defy history. The rationale of moving Bairstow up to five is simple enough. Bairstow has proved himself to be among England’s best five batsmen – by most estimations, indeed, he has been second only to Joe Root since 2016 – so should bat in a position that gives him ample opportunity to leave an imprint on the match.

That, at least, is the theory. But if Bairstow is to be a success in the dual demands of batting at five and keeping wicket, he will have to go against the overwhelming body of evidence in Test cricket, which shows that being a top-order batsman while keeping wicket is debilitating to batting performance.

Test cricket is simply too exacting, on the body and on the mind. Only 10 keepers have ever kept wicket in at least 12 matches while batting in the top five. And of the seven to have kept wicket in at least 20 Tests while batting in the top five, just three have averaged at least 35 when batting there.

Double trouble: is keeping harming Bairstow's batting? credit: Getty

AB de Villiers, unsurprisingly, was an exception – averaging 57, with seven centuries, when keeping and batting the top five. Yet even South Africa decided that ultimately this was not the best way to use his multifarious talents; that, in the long term, using a totemic batsman as a keeper risks undermining his returns.

Kumar Sangakkara averaged an outstanding 40.68 as a keeper batting in the top five – but an absurd 66.78 as a specialist batsman in the top five. So even with Sangakkara, Sri Lanka ultimately deemed that the trade-off wasn’t worth it: Sangakkara was able to keep while maintaining a fine average for a specialist batsman, but keeping prevented his batting reaching the stratospheric heights it did when he ditched the gloves.

That leaves only one Test keeper who was ever able to bat in the top five for an extended period without it significantly damaging his batting returns. Andy Flower averaged 52.45 over 51 Tests for Zimbabwe batting in the top five – even more remarkable considering that he played in a weak side, so would be fielding long and batting early. Flower stands alone – and even he averaged more as a keeper when not batting in the top five. Doing this double shift is simply extraordinarily difficult.

Mark Waugh of Australia hits out as Andy Flower watches credit: Getty

Bairstow has already shown as much during his matches as wicketkeeper. When he keeps and England bat first, he averages an outstanding 59.00 in the first innings. But when he keeps and England bowl first, he only averages 29.18 in the first innings.

As a batsman-keeper, Bairstow in his Test career has not been one player so much as two. The first is one of the best batsmen around; but, as soon as Bairstow keeps in a Test, he metamorphoses into just another mediocrity in England’s top six. Overall, Bairstow has 1,357 runs at 59 as a batsman-keeper before he has kept in the match, including all five of his Test centuries; but just 1,210 runs at 32.70 when he bats in games that he has already kept wicket in.

Even this great found himself stretched thin: Sri Lanka's Kumar Sangakkara credit: AFP/Getty Images

None of this is an indictment of Bairstow, a cricketer who trains relentlessly and throws everything of himself into each challenge. It is, instead, simply an extreme manifestation of how onerous being both a top-order batsman and keeper is in Test cricket. Across all Tests in the last decade, keepers average 40.22 in the first innings when their teams bat first, but only 35.30 in the first innings when their teams bat second – even though the average first-innings scores for teams batting first and second are virtually identical.

Given the paucity of high-calibre batsmen in England’s side, all of this suggests that Bairstow has been misused: not because he has been batting too low while keeping but because he has been keeping at all. He is, in short, in danger of being a successor to Alec Stewart. For all the fine innings he played while keeping, doing so prevented Stewart from becoming one of the leading Test batsmen of his age: he averaged 33.06 as a keeper batting in the top five, but 47.17 as a specialist batsman in the top five, greater than any other England cricketer in his era. Unlike then, England now have, in Jos Buttler, another wicketkeeper being picked as a specialist batsman.

Bairstow is a cricketer who wants to do it all, and relishes the challenge of both batting in the top order and keeping wicket. Yet from number five, he is not only tasked with bringing stability to England’s middle order – but also resisting one of the iron laws of Test cricket.