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The revelation has sparked fears terrorists may have infiltrated our armed forces.

MI5 agents already believe exBritish soldiers are fi ghting with Islamic State and may return to the UK to commit atrocities.

But the latest disclosure will fuel fears our services are being targeted by extremists.

Senior Ministry of Defence figures admit infiltration by potential terrorists is almost inevitable and is one of the reasons why security vetting is now treated so seriously.

A Freedom of Information request obtained by the Daily Star Sunday shows that in the last two years, 188 Army recruits were prevented from undertaking training for security reasons.

The recruits were all selected for training but had their applications rejected after they failed the security vetting process.

All recruits wanting to serve in the armed forces must undergo a series of background checks.

But additional counter terrorist checks are carried out on individuals with links to countries where a terrorist threat exists.

A senior defence source said the Territorial Army was especially prone to infiltration, particularly in areas such as Birmingham and Bradford where there are large Muslim populations.

The insider said: “The TA is desperate for recruits.You can pretty much turn up, fill in a few basic security vetting forms and then you are in. You can learn about fieldcraft, weapons handling and explosives very easily.”

Most recruits have access to small arms and undergo infantry training.

Sources also said terrorists could get greater benefi t from targeting selected units such as the Intelligence Corps, the Royal Engineers and logistics.

The TA’s Royal Engineers would give them access to explosives, while the Royal Logistics Corps would provide access to military fuel dumps and a fleet of tankers.

During the Ulster troubles, recruits with a Catholic background who came from Northern Ireland or the Irish Republic could face checks lasting months to ensure they had no links to terrorist groups.

The same checks are being applied to recruits with family or religious links to countries in the Middle East, Pakistan, Bangladesh and Nigeria.

The revelation comes months after it emerged terror chiefs had ordered jihadists to infi ltrate the British Army.

A manual used by Islamic State urged followers to join the Army and police to carry out attacks.

The manual explained how the atrocities committed in the Middle East – including the murders of British hostages David Haines and Alan Henning – were part of a wider strategy that includes plans to wreak mayhem in the UK.

The handbook, called the Management of Savagery, also revealed infi ltration operations had been going on for years.