THERESA May has admitted there is "a lot to be done" in the Brexit negotiations with Brussels amid suggestions Cabinet ministers believe talks on a future trade relationship could be delayed until Christmas.

The Prime Minister said there had been a constructive and positive start to the first phase of talks, focused on the so-called "divorce bill", citizens' rights and the Irish border.

But she did not directly address reports that Cabinet ministers involved in the negotiations have privately indicated they think progress on the second phase - focused on a post-Brexit EU trade deal - might not happen until December.

READ MORE: MP Swinson under fire over 'vanishing' election costs

In spite of predicting the "row of the summer" over the sequencing of negotiations, David Davis, the Brexit Secretary, in June accepted the European Union's proposed timetable.

The aim now for both sides is to make "sufficient progress" by October's European Council summit of EU leaders to get approval for talks on a future trade deal.

But commenting on reports that next month's federal elections in Germany could have an impact on the process, Mrs May told reporters in Mid Wales: "It's good that we've had a constructive, positive approach to the negotiations so far and those negotiations are continuing and we are working with the European Union.

READ MORE: MP Swinson under fire over 'vanishing' election costs

"There's a lot to be done. As a Government we have shown the work that we are putting into this, we have published recently just in the last few days a number of papers that set out our thinking on some of those key issues for the future relationship.

"We will develop a deep and special partnership with the European Union for the future that's good for the UK and it's good for the EU as well."

The Liberal Democrats seized on reports of a delay in beginning talks on Britain’s future trading relationship with the EU with their spokesman Tom Brake, saying they represented a “humiliating climbdown” for Mr Davis.

Pointing out how the UK Government’s intention was to have the talks on a future trade deal in parallel with the withdrawal negotiations, he said: “Once again, the bluff and bluster of Tory eurosceptics is being exposed to the cold reality of Brexit.

"We were told the EU would be begging us for a trade deal; now even the hard Brexiteers in this government are having to admit Brussels won't roll over just because the Germans sell us cars.”

READ MORE: MP Swinson under fire over 'vanishing' election costs

The London MP went on: "The UK could now be left with just ten months to negotiate a trade agreement before we crash out of the EU.

"The reality is no trade deal will be able to replace the benefits for jobs and living standards we enjoy as members of the single market and customs union," he added.

Meanwhile, further suggestions that the Home Office is drawing up plans to enable EU citizens to enter Britain without a visa requirement post Brexit were branded a surrender on trying to control immigration.

At present, all EU citizens are currently free to live and work in the UK without a permit.

It is suggested the Whitehall proposal for life beyond Brexit would mean free movement would still apply to EU citizens wishing to visit Britain but that if they wanted to work or settle here, then they would have to have a permit.

READ MORE: MP Swinson under fire over 'vanishing' election costs

The Home Office insists managing migration is about access to work and benefits as much as it is about the ability to control entry at a physical border.

But concerns have been raised about EU citizens disappearing into the black economy. There has already been criticism this week over the Government’s preferred option for having a soft border with no checks between Northern Ireland and the Irish Republic. It has been suggested this could provide a “backdoor” into Britain and create a “smugglers’ charter”.

Labour’s Ben Bradshaw, speaking on behalf of Open Britain, the campaign against a hard Brexit, said: "Nobody who voted to leave the European Union expected Brexit to mean Britain losing control of immigration, yet that is exactly what the government proposes.

"Restricting the right to come and work in Britain while leaving an open door for everyone else seems to be opposite of a common sense immigration system,” declared the Exeter MP.

"It will not restrict anybody coming here from Europe who does not intend to work and may push other EU nationals into the black economy."

READ MORE: MP Swinson under fire over 'vanishing' election costs

The former Culture Secretary said the proposed new system "offers little control while burdening British businesses with yet more red tape". He added that the Government should "put single market membership back on the table" instead.

Meanwhile, the Migration Watch pressure group said the Government’s plan was "sensible” and “proportionate" but claimed more money would have to be spent on immigration enforcement to deal with over-stayers.

The Home Office said: "Proposals for the future immigration system for EU citizens will be published in due course."