Boris Johnson has written to Labour leader Jeremy Corbyn to demand he “come clean” over what his position is on Brexit.
The prime minister said voters “deserve to have a clear picture of what each potential leader will do when it comes to Brexit”.
Ahead of the first TV debates – being staged by ITV – Mr Johnson warned any further delay, or possibly another referendum, risked destroying “all faith in our democratic process”.
In his letter, Mr Johnson says: “Your current position seems to be that you want to go back to square one.
“You want to throw out the great new deal we have reached with our European friends, and instead negotiate a whole new treaty from scratch.
“Even assuming the EU agrees to go back to the very beginning, this will take months and possibly years to do – under your proposals, 2020 will be lost to more dither and delay over Brexit.
“Voters also have the right to know: what would your supposed Brexit ‘deal’ actually back control of?
“For months you have refused to say what sort of ‘deal’ you want with the EU. Now the time has come for you to come clean, and explain what your plan really is.”