"When it comes to Brexit there is a very real risk of a Brexit no-deal by accident", he told a news conference alongside his German counterpart Heiko Maas.
Dominic Raab has insisted he will not "wallow in pessimism" about the Brexit process as Eurosceptics voiced concerns his department was being sidelined by Number 10.
Asked by committee member Jacob Rees Mogg about the changes, Robbins said there had been two teams of civil servants since his move from DExEU to the Cabinet Office - one advising the prime minister and one advising the Brexit secretary.
"I am going to bring to (Michel) Barnier and to the whole enterprise as much energy as I can".
"You can't have one side fulfilling its side of the bargain and the other side not, or going slow, or failing to commit on its side".
Calling on the United Kingdom to "respect this principle", Mr Barnier also reiterated that the EU remains open to agreeing a post-Brexit customs union with the United Kingdom, despite the prime minister having consistently ruled this out.
"So, I think we do need to make sure that there's some conditionality between the two". Welcome to the sunlit uplands of Brexit folks.
As Mr Raab, who has said a deal with the European Union can be reached by October, readied to return to Brussels for more Brexit talks on Thursday he signalled that Britain could withhold its £39 billion divorce bill if it did not get a trade deal in return.
"Britain will find that challenging but in the end we will find a way not just to survive but to thrive economically", he said.
"We are continuing to prepare the legislation needed to implement the withdrawal agreement in United Kingdom law and we will publish a white paper tomorrow setting out more details on this", Martin Callanan told the upper house of Britain's parliament.
On July 12, Mrs May put forward a model under which the United Kingdom would collect the EU's tariffs on goods entering the country, as part of a plan to keep trade with the bloc flowing freely after the split.
Central to the Prime Minister's plan, set out in a white paper a fortnight ago, is a "facilitated customs arrangement" under which tariffs charged at the border would be passed on to either the British or European Union authorities depending on the destination of imported goods.
Mr Raab repeated the Government's intention to finalise the withdrawal agreement, as well as a political declaration on future UK-EU relations, in October.
The financial settlement is an estimated figure that the United Kingdom is obliged to pay the European Union based on the various outstanding commitments that exist from over 45 years of European Union membership. He noted that 80% of the withdrawal agreement was already settled.