The Scots Guards, who have fought in nearly every conflict since the reign of Charles I, are now the most undermanned regiment in the UK, according to figures obtained under freedom of information law.
The Guardian request revealed that some British regiments are operating at almost 40 per cent below their required strength due to declining recruitment numbers.
Data from the Ministry of Defence shows numbers in Army infantry units have been consistently falling over the past five years, with information published quarterly by the ministry noting a 7.6 per cent drop in Army personnel on January 1.
But the Guardian analysis of the figures shows nine of 16 infantry regiments were 20 per cent below their required personnel level, four were 25 per cent below and the prestigious Scots Guards unit was 37 per cent below its target strength.
The infantry as a whole was found to be operating at 17 per cent below.
Defence Secretary Ben Wallace has been urged to address the issue.
Shadow defence secretary Nia Griffith was quoted as saying the “shocking trend” had to be halted.
She said: “At a time when our country faces an increasing number of threats, it is simply unacceptable for numbers to be falling year after year.”
Tory MP Bob Seely criticised the firm Capita, which began managing recruitment for the MoD in 2012.
He said: “Capita have not been a success. If you talk to people who are wanting to go into the Army, the most common way they describe it is shambolic and chaotic.”
But the MoD insisted the Army “continues to meet all its operational commitments to keep Britain safe”.
An Army spokesperson said: “Applications to join the Army are at a five-year high, with around 77,000 applications to join as a regular soldier alone in financial year 2018/19.
“We are fully committed to improving our recruitment process and we are working with Capita to address remaining challenges.”
Capita said: “The partnership is in the middle of a reset, which started last year but is already seeing excellent results. This includes the busiest quarter since the partnership started seven years ago, with 1,000 more enlistments in January to March than the same three months last year.”