Britain's borders were left exposed to terrorists last year after a Home Office computer system which screens passengers crashed twice in 48 hours, The Telegraph can reveal.

The eBorders system, which was put in place after the 9/11 terror attacks to protect the country from jihadists, ground to a halt in June last year.

The incident, which this newspaper has seen details of, was deemed so serious that Theresa May, the Home Secretary, was alerted by officials close to midnight.

The Home Office refused to reveal how often the system has crashed or whether there have been any outages since the incident.

Technicians worked through the night to fix the system amid fears from border officials that hundreds of extremists, convicts and illegal immigrants were arriving in the UK undetected.