As part of the EU's Brexit talk guidelines, Spain is set to be given the power veto a future trade deal if it is not given a say over the future of Gibraltar, the southern tip of 'Spain' which remains under British control and is home to some 30,000 Britons.

Papers setting out the EU's Brexit talks strategy say that the region will only be included in a post-Brexit trade deal if Spain agrees with the terms.

A source described as a senior EU official told The Guardian that, "The union will stick up for its members, and that means Spain now."

"Any extension of the deal to Gibraltar, which is a disputed territory, will require the support of Spain. Spain must approve the applicability of a future agreement to territory of Gibraltar. It recognises that there are two parties to this dispute," an EU source told the newspaper.

It was not mentioned in Theresa May's letter to Donald Tusk on Wednesday - which did include references to Scotland, Wales and Northern Ireland.

Gibraltar’s chief minister Fabian Picardo has warned against Gibraltar being used as a bargaining chip during Brexit negotiations.

A number of British MP's have already come out to condemn the inclusion of this clause in the EU's guidelines.

The region's corporation tax is only 10% and its economy is home to some 500 financial firms.

The 'Rock' - which has been controlled by Britain for 300 years - is also home to UK military bases.

In 2002 a referendum which would have given Spain and Britain shared control of the region was rejected by almost 99% of the population.

More than 90% of voters in Gibraltar wanted the UK to remain in the EU in May's referendum.