One of the UK's most senior policemen has said Britain should negotiate with al Qaeda in a bid to end its campaign of violence. Sir Hugh Orde, head of the Police Service of Northern Ireland, said he could not think of a single terrorism campaign in history that ended without negotiation. He is reportedly a front-runner to be the next commissioner of the Metropolitan Police. Sir Hugh told The Guardian that 30 years of tackling the IRA convinced him that policing - detecting plots and arresting people - was not enough alone to defeat terrorists. He said: "If you want my professional assessment of any terrorism campaign, what fixes it is talking and engaging and judging when the conditions are right for that to take place. "Is that a naive statement? I don't think it is ... It is the reality of what we face. "If somebody can show me any terrorism campaign where it has been policed out, I'd be happy to read about it, because I can't think of one." Sir Hugh admits that negotiating with terrorists means "thinking the unthinkable". He said some of the biggest risks his officers took were talking to people that "historically they would not have dreamed of talking to". He cites his 2004 meeting with Sinn Fein leader Gerry Adams as an example of how one-time enemies can become partners in peace. Asked if he was saying "we should talk to al Qaeda", Sir Hugh said: "I don't think that's unthinkable, the question will be one of timing." He said Irish terrorists still wanted to bomb the UK mainland but lacked the capability. They were still attempting to buy weapons but were disorganised, "psychopathic" and probably numbering no more than 200 people, he said.