The 78-year-old, who was MI5’s first female Director General, said: ‘The community has the responsibility to act as the eyes and ears, as they did during the war … where there were all these posters up saying the walls have ears and the enemy is everywhere.

‘There have often been indications in the community, whether it’s Muslim or anywhere else, that people are becoming extremists and spouting hate phrases.’

Dame Stella said security services had to prioritise the most dangerous threats because ‘thousands’ of people were being radicalised in Britain.

She said further terror attacks on the UK were inevitable unless the country became a ‘police state’.