BRUSSELS (Reuters) - European Union leaders will issue guidelines for chief Brexit negotiator Michel Barnier in March on the future relationship he should negotiate with Britain, regardless of whether London clarifies what it wants, a senior EU official said on Wednesday.

FILE PHOTO: Anti-Brexit demonstrators wave EU and Union flags outside the Houses of Parliament in London, Britain, January 30, 2018. REUTERS/Toby Melville/File Photo

This adds to pressure on the deeply split government of Theresa May to spell out what Britain expects from a future free trade deal with the EU after it leaves the bloc in March 2019.

EU officials said that if Britain failed to provide any more details on what it wanted by March, the guidelines would be less detailed, providing less certainty for British firms desperate for more clarity on their future business ties with the EU.

Some EU officials have also held up a potential delay in issuing the guidelines as a means of pressuring Britain to more quickly finalise talks on a withdrawal treaty and a transition period that is to follow Britain’s exit.

But the senior EU official, close to the Brexit process, said the completion of the withdrawal agreement was never a formal condition for producing the guidelines.

“It might be raised that ...the legal text of the withdrawal agreement (should be) on the table and maybe even an agreement in principle on the withdrawal agreement... (but) in our view it was not a pre-condition for having the guidelines in March,” the official said.

Since an agreement in December on the basics of Britain’s withdrawal, EU officials have been urging London to clarify what it wants from a transition period and a future relationship.

But the British government, split into supporters of a tougher and softer line to take, has so far been unable to make any proposals, other than sticking to the initial position that Britain no longer wanted to be part of the EU’s single market or customs union or respect European Court of Justice rulings.

These “red lines”, however, appear to be irreconcilable with Britain’s pledge not to re-introduce a physical border between Northern Ireland and Ireland or to give its companies, including banks, as full access as possible to the EU’s market.

The EU official said that in the absence of any new input from London by March, the guidelines for Barnier would simply be based on what Britain has declared so far.

“Some wishes have been expressed and on the basis of these wishes the guidelines will be prepared in March,” he said.

The negotiations between the EU and Britain on the future relationship are to end in October with a political declaration attached to the withdrawal treaty. The declaration will then be the basis of negotiating a proper free trade agreement once Britain ceases to be a member of the EU in March 2019.