People from outside the Commonwealth must currently live in Britain for five years and take British citizenship before they can sign up.
However, as the manning crisis in the Armed Forces deepens, a surge of interest from Polish immigrant workers has prompted some to call for a loosening of the rules.
Lt Col Paul Meldon, commander of regional recruitment in London, said a significant number of Poles had made inquiries and voiced interest about joining up.
“Currently, they can’t join up unless they live here for a few years and get a British passport – and it would need legislation to change that,” he told the Daily Mail.
“There is a precedent for having battalions of foreign soldiers in the British Army, in the form of the Gurkha regiments.
“Or there is the French approach, where they have the Foreign Legion.”
A loosening of the rules could make a large number of potential recruits available, he added.
Recent figures show the military is short of more than 5,500 troops.
In an effort to address the problem, the Army on Monday launched a new £2 million recruitment campaign.
Brigadier Andrew Jackson, Commander of the Army Recruiting Group, said the Army was on course to miss its annual recruitment target by about 10 per cent.
Brig Jackson revealed the news as he launched the To The Best campaign, which encourages the public to show their support for British troops.
The Telegraph has launched its own campaign to support British troops, calling on the Government to hold an annual Armed Forces Day.
Last month, government figures revealed a third of Army recruits were dropping out of basic infantry training.
The growing casualty rate in Iraq and Afghanistan and the low pay of trained infantry soldiers have been identified as factors persuading recruits to leave early.