Published: 9:01 AM July 27, 2018 Updated: 8:42 AM September 18, 2020

Theresa May's bid to win European allies on Brexit has suffered a setback after she was warned she will struggle to find "loopholes" in the EU's approach to talks.

The prime minister will discuss her plan for leaving the EU with Austrian chancellor Sebastian Kurz and Czech counterpart Andrej Babis as she seeks to build alliances as the clock ticks down to the March 2019 Brexit date.

Both the Austrian and Czech governments have been critical of aspects of EU policy, particularly on migration, and Mrs May hopes she can use internal divisions within the bloc to push for a more flexible approach from Brussels to the Brexit negotiations.

But in another blow for the beleagured PM, Czech state secretary for European affairs Ales Chmelar today insisted there was unity behind Michel Barnier's approach to the talks.

EU chief negotiator Mr Barnier dealt the prime minister a serious blow by rejecting a key plank of her Brexit strategy yesterday.

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Central to Mrs May'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 EU authorities depending on the destination of imported goods.

But Mr Barnier yesterday made clear that was not acceptable to Brussels.

Mr Chmelar gave his backing to Mr Barnier's position, telling BBC Radio 4's Today programme: "There is a clear problem with the fact that the EU will not have a mechanism to control its borders and it would be delegated - without any EU control - to a third country, which would be Britain after March.

"So, that is the key principle. But also there is a larger general principle... it is almost physically impossible to have, at the same time, full regulatory autonomy on one side and full market access.

"There needs to be a certain balance between the rights and obligations in those terms."

He also indicated that Mrs May's hopes of finding support from her counterparts during the talks in Salzburg may be muddle-headed.

Mr Chmelar acknowledged the Czechs had some concerns over the way the EU worked but insisted the bloc remained united in its approach to Brexit talks.

"The fact that we are maybe critical of some aspects of EU policies, be it in migration or be it in other areas, does not meant that we wouldn't stand behind a very strong position on the integrity of the single market," he said.

He said the Czech stance in relation to Brussels on some areas of policy did not allow "a more open position for trying to find loopholes in the EU position" on Brexit.

The UK will seek to highlight the potential impact of the failure to reach a Brexit deal on individual economies across the bloc, hoping that domestic political interests may result in pressure from EU national leaders on the Brussels bureaucracy to soften its stance.

But Mr Chmelar said the EU's leaders had been fully involved in approving the mandate given to Mr Barnier and stressed that while the UK was an important trading partner it was not as vital as the Czech Republic's neighbouring countries.

But he acknowledged that "every member state of the EU is, to a certain extent, worried" about the prospect of a no-deal scenario.