Former British Prime Minister Tony Blair and his successor Gordon Brown may have had a tempestuous decade together in government, but Blair's wife Cherie says they will be "friends forever."

Brown had agreed that Blair should run as leader of the Labor Party in a deal struck in 1994, on the proviso that Blair would eventually step aside but Brown's impatience to take over as prime minister eventually soured their relationship.

"Their friendship goes back a long way and I'm sure they will be friends forever," Blair said in New York, where she was promoting the US release this week of her autobiography Speaking for Myself.