Britain has almost as many overseas volunteers serving in its armed forces as the French Foreign Legion, The Herald can reveal.

The number of soldiers from Commonwealth and other countries who enlisted in the UK's Army, Navy and RAF rose by 790 last year to 7240. By comparison, the famous Legion Etrangere has 7600 men in its ranks.

If the 3000 Gurkhas were included, Britain's foreign legion would outnumber that of France and Spain, which deliberately recruit foreigners for military service.

The vast majority of Commonwealth volunteers have joined the Army. They include 2030 Fijians, 600 Zimbabweans and 460 from the tiny Caribbean island state of St Vincent and the Grenadines.

There are also 880 from South Africa, 140 from Kenya and 170 from Australian and New Zealand. Another 80 are from Canada. Almost one in 10 of the soldiers in the Royal Regiment of Scotland is Fijian. High unemployment at home, almost 25% in most Caribbean islands, and political or social unrest appear to be the main driving forces behind the enlistments.

The number of Caribbean volunteers has shot up, with the St Vincent contingent rising from 280 in 2006 to 460 last year. South African volunteers rose from 720 to 880, while Trindad and Tobago's contribution to British numbers increased by almost one-third from 70 to just over 100. Zimbabwe, now in economic and political meltdown, produced a 20% rise.

With almost every battalion in the Army an average of 90 men below frontline "bayonet strength", the influx of willing volunteers means there are foreigners in most units, with the highest concentration in the hard-pressed infantry.

The MoD admits the Army is 3800 men below complement, a shortfall worsened by the number of experienced soldiers of all ranks choosing to leave, largely because of the family pressures resulting from repeated combat tours in Iraq and Afghanistan.

Figures obtained by The Herald show the Royal Armoured Corps, the Army's 11 tank and reconnaissance units, are 590 men short - the equivalent of a regiment.

Even Prince Harry's unit, the Household Cavalry, are 65 troopers under-recruited. The Royal Scots Dragoon Guards, which is sending a 120-strong squadron to Afghanistan to support a new spring offensive against the Taliban, is 104 below its 587 "operational manpower liability".

Proposals drawn up last year by the Army general staff, headed by General Sir Richard Dannatt, are in favour of imposing a ceiling on the number of non-UK volunteers.

Senior officers are said to be worried the Army could be seen as employing too many "mercenaries" and are keen that it should reflect British "norms and values".

The MoD said a decision on limiting overseas volunteer numbers had not yet been taken. A spokesman added: "The Army has a long and successful tradition of employing and integrating overseas personnel and we have no wish to discontinue this practice."