Britain's borders are almost undefended against terrorists and criminals using small boats and planes, a watchdog has found.

David Bolt, the Chief Inspector of Borders, disclosed failings which could give back-door entry to jihadists.

There are just three Border Force patrol vessels for the whole coast, less than one-twentieth of France’s capability. Two more were either tied up in port or deployed to the Mediterranean refugee crisis. Aerial surveillance was scrapped in January to save money.

Crews on small vessels such as yachts, tugs and motorboats or “general maritime” should notify officials of their arrival on a phone line but just 177 out of tens of thousands did in 2014.

The report admits that there is “no reliable data for the number of general maritime arrivals in the UK” and “no systematic collection of information about any aspect of general maritime”.

Almost no information is known about the names of passengers on any small vessel, the inspectorate was told.

The patrols had almost no systematic tasking and only one crew, which is based in Harwich and Felixstowe, regularly boarded any suspect vessel.