EU officials have downplayed the prospects of Britain being given legally-binding guarantees on the Irish backstop at tomorrow's EU summit in Brussels.

One diplomat suggested that the British Prime Minister Theresa May will ultimately be offered little more than a statement that "clarifies" aspects of the Withdrawal Agreement and the accompanying Political Declaration.

Against the backdrop of the leadership challenge in Westminster, British ministers are reported to be looking for legal guarantees that the backstop will be temporary.

However, EU diplomats have poured cold water on the idea that Mrs May could be offered some kind of legal mechanism to reinforce the temporary nature of the backstop.

One source has suggested that attitudes in Brussels have hardened as the day wore on and Mrs May's position as Conservative Party leader looked less perilous.

The source suggested that so long as Mrs May looked in danger of being toppled there was more of an appetite to "help" her in terms of offering assurances on the backstop, but that that appetite receded when she looked increasingly likely to survive the challenge.

Mrs May will address EU leaders late tomorrow afternoon on day one of the summit and following dinner, the EU27 - without the British prime minister present - will discuss her requests.

A leaked draft of a five-paragraph statement to be agreed by EU27 leaders suggests that the EU "stands by this [withdrawal] agreement and intends to proceed with its ratification. It is not open for renegotiation."

Further paragraphs will reflect the EU's desire for a close relationship with the UK post-Brexit and that the backstop is not the EU's preferred option.

The draft statement - which is subject to further changes at the summit - will say that it is the EU's "firm determination" to work towards a subsequent trade agreement by December 2020 which will mean the backstop is not needed.

According to one diplomat, the EU will offer little more than to highlight what is already in the deal.

"The Withdrawal Agreement and the Political Declaration are set," said the source. "It is a compromise. This is what's on the table. We're not sure the Political Declaration has been studied in detail.  There are certain aspects of the Political Declaration we could highlight.

"Additional written legal guarantees have not been discussed."

The source dismissed precedents such as a declaration secured by the Dutch Prime Minister Mark Rutte in 2016 on the impact of the EU-Ukraine Association Agreement, and the so-called February Settlement of concessions offered to David Cameron ahead of the EU Referendum and which was lodged as a legal document with the UN.

No legal mechanism was required in this case, said the source.

Asked if the EU might be willing to change aspects of the backstop, the source said: "We cannot soften on the backstop. This is not something like a real estate deal. This is about the internal market of the EU which we can't be flexible on. This is not negotiable."