Europe's open borders are putting Britain's security at risk, former police chiefs have warned after it emerged that the terrorist behind the Berlin Christmas market attack travelled unhindered through three countries before being killed in Italy.

Anis Amri, the most wanted man in Europe, travelled from Berlin to the French Alps and then onto Italy without being stopped at any point on his 1,000 mile journey.

It was only after a chance encounter outside a suburban station at 3am that he was shot dead by a rookie Italian police officer who recognised him.