Jacqui Smith began the toughest week of her ministerial career yesterday trying to defend herself after saying that the streets of London were too dangerous to walk alone at night.

The Home Secretary had planned to introduce an initiative on knife crime, strike a tough position on police pay and set out her arguments for detaining terrorist suspects without charge for 42 days.

Instead, she called the Government’s law and order record into question by saying that there were parts of the capital where she would not venture on her own after dark. “I just don’t think that’s a thing that people do, is it really?” she told The Sunday Times. David Davis, the Shadow Home Secretary, said her remarks were “an astonishing admission”.

An aide said later that the Home Secretary, who has full-time police protection, was not afraid to go out and had recently bought a late-night kebab in Peckham, South London.

The apparent gaffe put Ms Smith on the back foot at the beginning of a week when the new Counter-terrorism Bill is published and up to 15,000 police officers will march past the Home Office in protest at her decision not to meet their pay award in full.

It also overshadowed her support for airport-style metal detectors to prevent pupils carrying knives into inner-city schools. Ms Smith, a former teacher, said: “It’s a good idea if we look at the ways in which, in some schools, it might be appropriate.”

The police demonstration is due to take place on Wednesday, the day before the House of Commons votes on a proposal to give MPs a 2.8 per cent pay rise. On Friday the latest terrorism legislation will be published, which will include proposals to provide for detention of terrorist suspects for up to 42 days.

Ms Smith told the BBC that the proposal was to create a “reserve power” for which the police could apply in the event of complex or multiple plots or after a national emergency. She said: “The 42 days is not some sort of target, it’s a safeguard. It’s an absolute maximum.” The Government hopes that it can win that debate by exploiting emerging Tory divisions over the issue.

Gordon Brown, interviewed in India, said he believed that it was possible to build a cross-party consensus on the use of extended detention in emergency situations. Labour’s belief that its opponents are divided appeared to be confirmed by Mr Davis. He told The Sunday Telegraph: “There have been colleagues who have said, ‘This is a bit dangerous, you’re taking a chance with public opinion’.”

Westminster political blog

Times Recommends

• I was not the underdog, says Frost
• First-timer scoops Booker with Indian tale
• Churchill 'bribed Franco's generals'