“I was surprised by what they both said and I think their views will collide with the reality when whichever one wins, starts dealing with a Parliament which may be more difficult than they think.”
Both Mr Johnson and his rival Jeremy Hunt have suggested they could take Britain out of the EU without a formal exit deal.
However a majority of MPs may attempt to block a no deal Brexit in Parliament.
Ahead of the 2016 EU membership referendum Ms Rudd was a prominent ‘Remain’ campaigner.
Separately the Office for Budget Responsibility, the Government’s official forecaster, is expected to predict Britain will fall into recession if it leaves the EU this year without an exit deal.