Hannigan has not spoken of his role in the Northern Ireland peace process but he is the only British civil servant involved to be singled out in Tony Blair's autobiography, where Blair describes him as "a great young official who had taken over as the main Number 10 person [on Northern Ireland]" and cites him as an example of creativity. Hannigan appears regularly in other accounts, notably by Blair's Chief of Staff Jonathan Powell, attending private crisis meetings with Irish Republican leaders, including Gerry Adams and Martin McGuinness, at Stormont Castle and Clonard Monastery. Powell describes his key role in brokering agreement with Ian Paisley and the Democratic Unionist Party during and after the St Andrews Agreement talks. He is described as chairing the first meeting between the DUP and Sinn Féin and designed the diamond shaped table which brought Adams and Paisley together at a public meeting on 26 March 2007, which is widely regarded as marking the end of the Northern Ireland 'Troubles'.