Former UK prime minister Gordon Brown has said that Ireland will be united in the long term, describing it as inevitable but adding that it would be a long process requiring agreement.

In an interview, Brown, who was chancellor when the Good Friday Agreement was signed in 1998 and prime minister when justice powers were devolved to Northern Ireland in 2010, said the geographical link between Northern Ireland and the Republic made unification logical.

He said: \"In the long term, Ireland will be united.\" He added that it would be \"a long process where people have got to come together and find a way of agreeing\".

Brown contrasted his stance on Northern Ireland with his opposition to Scottish independence, arguing that Scotland was geographically, economically, socially and culturally linked to the rest of the UK.

The comments come as debate continues over when a border poll might be called. Letters to the Irish Times have called on Northern Ireland Secretary Chris Bryant to set out criteria for calling a referendum, suggesting that a majority vote in the Northern Ireland Assembly in favour of Irish unity could be one trigger.

Under the Belfast Agreement, the Northern Ireland Secretary has the power to call a border poll if it appears likely that a majority would vote for a united Ireland.

Brown's remarks are notable given his longstanding opposition to Scottish independence and his role in the peace process.