Asked if he thought his son, Boris Johnson, could become the next Prime Minister in the wake of a Brexit vote, Stanley Johnson replied he would be happy if anyone in his family is considered to have done a "useful job".
The chairman of Environmentalists For Europe who supports a remain vote, was campaigning in Bicester alongside Green Party MP Caroline Lucas, and former acting Labour leader Harriet Harman.
Mr Johnson also praised David Cameron's visit to Rainham Marshes Nature Reserve and statement on protecting the habitats of birds. However, Ms Lucas pointed out that should the UK vote to Leave the EU, Mr Cameron may no longer be Prime Minister.
The Green Party's Caroline Lucas has retained her Brighton Pavilion seat.
Green Party MP Caroline Lucas MP has been found not guilty at Brighton Magistrates' Court of obstructing a public highway and a public order offence during an anti-fracking protest at Balcombe, West Sussex.
ITV News Correspondent Martin Geissler reports:
Green MP Caroline Lucas told the court she felt it was important to protest about fracking to prevent the UK from being locked into using more fossil fuels.
Ms Lucas said: "I'm haunted by the idea that my children and my children's children will turn round to me and say, 'What did you do about this overwhelming threat?'"
Her co-defendants were also cleared of both charges against them. They were Josef Dobraszczyk, 22, from Bristol; Ruth Jarman, 50, from Hook, Hampshire; Sheila Menon, 42, from north east London; and Ruth Potts, 39, from Totnes, Devon.
Green MP Caroline Lucas has promised to continue her fight to end fracking after being found not guilty of obstructing a public highway and a public order offence.
"We will continue to campaign to end fracking and only celebrate when our world is on the path to a clean energy future," Ms Lucas said outside court.
She was arrested outside energy company Cuadrilla's exploratory oil drilling site in Balcombe, West Sussex, in August last year.
Speaking outside court Ms Lucas said: "We are pleased that the court upheld our rights to peacefully protest against fracking but the judgment is not a victory or cause for celebration."
Brighton Pavilion MP Caroline Lucas was arrested outside energy company Cuadrilla's exploratory oil drilling site in Balcombe, West Sussex, last August 19.
She was among a group of protesters who had linked arms outside the site, which had become a national focal point for anti-fracking protests.
During the trial at alongside four co-defendants, Lucas, 53, said she "wanted to express solidarity" by protesting peacefully. She was found not guilty of the two charges she faced - wilful obstruction of a public highway and breaching an order under Section 14 of the Public Order Act.
Green Party MP Caroline Lucas has been found not guilty at Brighton Magistrates' Court of obstructing a public highway and a public order offence during an anti-fracking protest at Balcombe, West Sussex.