Theresa May is coming under fresh pressure over Brexit on the eve of the Conservative party conference.Foreign Secretary Boris Johnson has again intervened on Brexit, setting out four conditions he says are necessary.
Speaking to the Sun, Mr Johnson insisted any transition period after Britain leaves the EU should not last "a second more" than two years.
Jeremy Corbyn said Mr Johnson's position threatened a trade war with the EU, which could impact on jobs.
The prime minister will be seeking to reassert her authority as she goes into her first party conference since she lost her government's majority in the general election.
It also comes after six months of Brexit negotiations in which there has been no significant breakthrough.
BBC political correspondent Jonathan Blake says Mrs May must take the agenda back to her priority: the economy.
Our correspondent says the timing of Mr Johnson's latest comments was "no accident", coming as Conservatives gather in Manchester for their annual conference, which starts on Sunday.
In his interview with the Sun, Mr Johnson called for four conditions for Brexit, which were then described by the paper as his "four red lines": Transition period must be a maximum of two years
- UK must refuse to accept new EU rules during that period
- No payments for access to the single market after the end of the transition period
- UK must not agree to shadow EU rules to gain access to the single market
Mr Johnson said: "The crucial thing I want to get over to Sun readers about Brexit is that it is going to be great and we need to believe in ourselves and believe we can do it. It is unstoppable."
He also touched on other subjects in the interview - calling for a faster increase in the minimum wage and for public sector pay rises.
While he dismissed suggestions of any leadership ambitions, his comments are likely to fuel speculation that he is still positioning himself for the top job.
Lib Dem leader Sir Vince Cable said the foreign secretary's comments sent a signal to EU negotiators that the "strings were being pulled by others".
"Senior Conservatives are displaying an abject failure to act together in the national interest and seem more motivated by selfish, personal ambition."