After more than a century of having their clean-shaven chins inspected, soldiers and officers in the British army will be allowed to grow beards.

The change in policy is not a chance for a hirsute free-for-all, however, as facial hair will be strictly monitored for length and grooming.

A message to troops was issued with an update that allows for neat growth over the Easter break. According to its terms, only a full beard is allowed. It must be between 2.5mm and 25.5mm long and trimmed off the cheekbones and neck. The policy stipulates there can be “no patchy or uneven growth” and “no exaggerated colours”.

The Times reported the decision had to be approved by the king, who gave his go-ahead on Thursday.

The navy has long allowed beards, and the air force lifted its ban in 2019. But the army had maintained a strict policy, allowing facial hair growth only for health, religious or operational reasons.

Last year, the army announced a review, and the vast majority of servicemen and women said they wanted the rule changed.

The new policy was announced in a four-minute video message to troops, according to the Times. It reported the army’s most senior noncommissioned officer, Paul Carney, saying: “Getting to an outcome has taken a bit longer than expected due to the larger number of stakeholders that were involved, including his majesty the king, our politicians and our allies. CGS [chief of the general staff] has taken account of your views and has decided the appearance policy will change, with our officers and soldiers being allowed to grow beards.”

For more than a century, the only facial hair allowed day-to-day in the army has been a neat moustache. While soldiers were allowed to grow beards for operational reasons – for example on covert missions or when fighting in Afghanistan – they had to shave them off on return.

The defence secretary, Grant Shapps, said in December that banning beards in the army was “ridiculous” and it was time to modernise.

“The armed forces get terribly pernickety about whether people have beards or not. Nowadays people have beards. How is it we are still struggling with recruitment and then arbitrarily saying you can’t join [if you grow a beard]. It is ridiculous. It is time to modernise,” he said in an interview with the Times.

An army spokesperson said: “Over the last few months, we’ve been conducting a review of our policy on personal appearance. An extensive audience of regular officers and soldiers, reservists, full-time reserve service staff and veterans have taken the opportunity to provide their views.

“Army leadership have reviewed the findings and the chief of the general staff has directed that the appearance policy will change, and officers and soldiers will be allowed to grow beards. We have listened to our people and acted.”