Britain's immigration officers have been told they are not allowed to sport stubble at work.

Dress code guidance published by the Home Office on Tuesday advised staff that an "unshaven or stubble appearance" is not permitted - although full beards and moustaches are allowed.

Should a worker wish to grow facial hair, they must do so "at a time that minimises the period when you present an unprofessional image," according to the advice.

The Home Office said the rules are specifically for Immigration Enforcement's Criminal and Finance Investigation(CFI) teams, who have a public-facing role. A spokesman for the government department added: "There is no Home Office formal dress code."

Immigration enforcement staff work at airports and sea ports across the country to prevent illegal migrants entering the country.

The dress code also bans hooded jumpers, denim jeans and miniskirts should. Dresses above knee length, flip-flops and "revealing" clothing such as low cut tops are "not considered smart", the diktat says.

It sets out a non-exhaustive list of items that are not considered smart, including denim jeans, T-shirts, frayed or torn clothing, sportswear including football and rugby shirts, and Lycra - although leggings can be worn with dresses or long smart tops.

Other items to be avoided include shorts, flip-flops, miniskirts or dresses above knee length, "inappropriate revealing" clothing, baseball caps or hats, "underwear as outerwear" and hooded or strapless tops. Allowances are made for covert operations where it is not suitable to dress formally.