Wolfgang Schauble is a key ally of German Chancellor Angela Merkel

Britain could be forced to write cheques to Brussels until 2030 despite leaving the EU, the German finance minister has warned.

Wolfgang Schauble delivered his blustering warning as Theresa May flew into Berlin for talks with Angela Merkel and other world leaders.

Mr Schauble said post-Brexit Britain would be bound by tax rules restricting it from granting incentives to keep investors in the country.

He also insisted there will be no special deal to curb freedom of movement if the UK wants to remain part of the common market.

Signalling that the bloc is determined to take a tough line in looming negotiations, Mr Shauble - a key ally of Mrs Merkel - said: 'Until the UK's exit is complete, Britain will certainly have to fulfil its commitments.

'Possibly there will be some commitments that last beyond the exit… even, in part, to 2030.'

Mrs May is expected to hold talks with Mrs Merkel and US president Barack Obama - who is on a farewell tour before handing over to Donald Trump in January - during her visit to Berlin.

The mini-summit will also be attended by the leaders of France, Italy and Spain.

Although Brexit is not on the agenda for the talks, the Prime Minister is likely to discuss the issue with European counterparts.

Germany's hard line approach comes after French President Francois Hollande said in October that Britain must pay a price for severing its ties to Brussels.

Mr Schauble said freedom of movement was a core part of the single market and changing the key principles of the bloc would hit financial services companies.

'There is no a la carte menu,' he said. 'There is only the whole menu or none.

Prime Minister Theresa May is in Berlin today for meetings with international counterparts including Mrs Merkel and outgoing US President Barack Obama

'Without membership of the internal market, without acceptance of the four basic freedoms of the internal market there can, of course, be no passporting, no free access for financial products or for financial actors.'

Mr Obama yesterday voiced hope that Brexit negotiations would be 'smooth and orderly'.

The US president notoriously waded into the EU referendum campaign earlier this year by suggesting the UK would go to the 'back of the queue' for a trade deal with America if it cut ties with Brussels.

He said after meeting Mrs Merkel in Berlin: 'I hope that the negotiations over Britain's withdrawal from the EU will be conducted in a smooth and orderly and transparent fashion, and will preserve as much as possible the economic and security relationship between the UK and the EU.'

He added: 'I think the European Union is one of the greatest achievements of the world.

'You have to preserve those achievements and fight for them. You can't take them for granted.'