These are the 3 issues which could still derail Theresa May's Brexit deal

• Theresa May heads to Brussels on Wednesday evening in a frantic attempt to wrap up the final details of her Brexit deal.
• Negotiators are trying to finalise a document which lays out aspirations for the future UK-EU relationship, but it's proving more difficult than expected.
• A planned EU summit on Sunday could be cancelled because both sides still haven't reached a breakthrough on crucial future relationship issues like fishing and Gibraltar, according to reports.

LONDON - Theresa May will head to Brussels for the second time this week Saturday with the hope of winning agreement for the final text of her Brexit deal. Negotiators have already agreed on the 585-page text of the divorce deal, formally called the Withdrawal Agreement, which covers thorny issues like the size of the UK's exit payment and the Irish backstop mechanism.

Attention is now on wrapping up the final text of the so-called political declaration, a much shorter document which will detail the UK and EU's aspirations for their future relationship. Unlike the withdrawal deal, it won't be legally binding but it will act as an important statement of intent from both sides.

However, some issues which the political declaration covers are proving to be more difficult to resolve than negotiators had anticipated, with reports on Wednesday afternoon that a planned EU summit for Sunday could be cancelled due to a lack of progress on issues connected to the UK's future relationship.

That could spell disaster for Theresa May. She had hoped to wrap up all details of the deal so that EU leaders could sign off her deal at the planned summit on Sunday. Here are the key issues which are holding back talks.

1. Gibraltar

The tiny territory of Gibraltar poses an outsized problem for Brexit negotiators. The rocky outpost on the southern tip of Spain has been a British territory for three centuries, and its service-based economy relies heavily on the free flow of workers across the border from Spain, which account for around half its workforce.

Gibraltar is a self-governing territory with 34,000 residents, most of whom are British citizens and 97% of whom voted to remain in the European Union in 2016. Equally, Gibraltar is physically connected to Spain and mainland Europe and has close links with Spain, which frequently challenges the UK's legal claim to the territory.

The UK would be happy enough not to discuss the future of detail in too much detail in the political declaration. But Spain's Prime Minister Pedro Sánchez has said Spain will reject the draft Brexit deal without a clarification of the text on the status of Gibraltar.

"As things stand today if there are no changes regarding Gibraltar, Spain will vote no on Brexit," said Sánchez on Tuesday.

Article 184 of the draft Brexit deal says the UK and EU will "negotiate rapidly the agreements governing their future relationship" during the transition period from March next year. But Spain wants much more clarity than that and insists it should be able to negotiate the future of Gibraltar bilaterally with the UK.

A European Commission spokesperson this week re-stated the EU's pledge that no Brexit agreement between the UK and EU could apply to Gibraltar without the agreement of Spain and the UK. It's a big issue which needs to be resolved quickly.

2. Fishing

Fishing is a highly contested area between the UK and EU. Britain wants the political declaration to declare that Britain is an "independent coastal state" which will negotiate EU access to its waters on an annual basis.

However, France, Denmark, the Netherlands, and Belgium want the language to state that continuing current arrangements for fishing access will be a precondition of a full UK-EU trade deal across all sectors. Quota shares of fish are currently allocated according to a formula, to the anger of British fisherman who say that fishing vessels from elsewhere in the EU have too much access to British waters.

3. Future trade

Above all, Theresa May sees the political declaration as an essential tool in the bid to sell her Brexit deal to sceptical Tory MPs.

To that end, she wants to include some particularly ambitious language on the future trade relationship. That provision could, she calculates, persuade her colleagues that the controversial "backstop" plan to avoid a hard border in Ireland will never be needed.

But countries including Germany, France and other close trading partners of the UK oppose any language which will raise false hopes that the UK could negotiate single market membership for goods, the Financial Times reported.

The EU has repeatedly rejected such proposals as seeking to "cherry pick" elements of the single market as part of May's so-called Chequers plan for leaving the EU. They will resist any attempt by May to leave the door open for this to go ahead in future talks.

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