Ken Clarke has asked David Cameron his final question as prime minister at PMQs.
He paid tribute to David Cameron's "wit and humour" and urged him to remain an "active participant".
Cameron joked that Clarke's first act as chancellor was to fire him as a special adviser.
He said Clarke had demonstrated "great wisdom, thoughtfulness and balance" during his time in the coalition government.
Speaking in Rushcliffe, veteran politician Ken Clarke has told ITV News that every Conservative MP is bound to be happy with the exit poll results, but that it is far too early to be speculating.
He said the East Midlands is going to be critical tonight with a lot of places surrounding Rushcliffe too close to call.
The Minister of State for International Development Alan Duncan has left the government.
Mr Duncan steps down after four years in the role.
Veteran minister and MP for Rushcliffe, Ken Clarke, has retired from the Government, sources close to him said.
He had already been demoted in the 2012 reshuffle, losing his post as justice secretary following a series of clashes with Home Secretary Theresa May.
Now the 74-year-old Nottinghamshire miner's son has quit as minister without portfolio, concluding a career which saw him hold government posts under four different Conservative prime ministers.