In a letter to the Prime Minister, Labour's Leeds Central MP Mr Benn pointed out that he had told the Commons he would set out his plan "long before" the 30-day timetable suggested by Chancellor Angela Merkel when they met in August.
However, Mr Benn said that with just four days to the 30-day deadline, EU Commission president Jean- Claude Juncker had made clear that such proposals "have not yet been made" by the UK side.
The European Union's frustration with Boris Johnson about his Brexit strategy was laid bare today after the Prime Minister met Mr Juncker. Mr Johnson and the European Commission president sat down for their first face-to-face talks in a restaurant in Mr Juncker's native Luxembourg.
Following their talks, the commission said Mr Johnson had still not made legally operational proposals to replace the backstop - the controversial contingency measure which keeps the UK closely tied to EU rules to prevent the return of a hard border with Ireland.
Luxembourg's Prime Minister Xavier Bettel went further, warning that EU citizens were facing mounting uncertainty due to Brexit while standing next to an empty podium after Mr Johnson pulled out of a joint appearance.
"You can't hold their future hostage for party political gains," Mr Bettel said.
Gesturing to the empty space where Mr Johnson should have been, Mr Bettel said: "Now it's on Mr Johnson - he holds the future of all UK citizens and every EU citizen living in the UK in his hands. It's his responsibility. Your people, our people, count on you - but the clock is ticking, use your time wisely."
In his letter to the Prime Minister, Mr Benn wrote: "I would be grateful if you could confirm when you intend to publish your proposals for an alternative to the backstop so that they can be scrutinised by the Select Committee, MPs and the public.
The piece of legislation Mr Benn authored - known as the Benn Act - passed by Parliament after MPs seized control of Commons business requires the PM to seek an extension to the Brexit process if a deal has not been reached by October 19.
Foreign Secretary Dominic Raab suggested earlier today the Government was still examining the implications of the legislation.
"The UK Government is always going to behave lawfully," he told BBC Radio 4's Today. At the same time, the legislation that was required, the surrender bill, is deeply, deeply flawed."