Labour has made an official complaint to the EU after a leaked document allegedly suggested officials were being told to discriminate against British firms when handing out multi-billion pound contracts.

The party’s international trade spokesman Barry Gardiner told The Independent the document represented an “appalling revelation” that had been missed by Theresa May’s government while it focussed on fighting an election.

Mr Gardiner has now lodged a “maladministration” complaint with the European Ombudsman, after the leaked document indicated European Commission officials had told staff to avoid “unnecessary additional complications” with Britain before Brexit.

The Labour frontbencher said: “It shows that officials are telling companies to actively discriminate against the UK. That is an appalling revelation.

“The Commission, are supposed to be the guardian of the treaties, and the guarantor of fair treatment.

“They should know that this sort of discrimination is against EU rules. While we are still a member of the EU we must be treated equally as a member state, and this means there can be no discrimination against British companies.”

He argued that Ms May and her government had “dropped the ball” in failing to properly respond, because they are “distracted by the general election”.

Mr Gardiner went on: “Theresa May called this election for petty party political advantage and it is the national interest that is now suffering.”

A government spokeswoman made clear that the UK remains a member state of the EU, subject to all the rights and obligations of membership.

She said: “UK organisations, businesses and universities should be in no doubt that they should continue to bid for competitive EU funds while we remain a member of the EU and we will continue to work with the Commission to ensure payment when funds are awarded.

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“As part of the negotiations, we will also carefully consider how best to maintain our ability to share and protect EU data with other EU member states, to ensure we reach an agreement that works in the interests of both the UK and the EU.”

The note leaked to the Financial Times earlier this week, was sent a week after Ms May triggered Article 50 and was signed by Alexander Italianer, the Commission’s secretary-general, Martin Selmayr, Jean Claude Juncker’s chief of staff and Michel Barnier, the EU’s Brexit negotiator.

It outlines how Britain could in practice end up losing out on money and influence, even while it still retains the legal rights and obligations supposed to be enjoyed by members states .

Where legally possible, the Commission and its agencies will be expected in all activities to “take account” of the fact that Britain may be “a third country” within two years, including in appointing staff and in awarding direct contracts.

It stated: “Apart from the legal requirement for a contracting party to be established in the EU, there may be political or practical reasons that speak in favour of contracting parties established in a specific member state, not only at the conclusion of the contract, but also throughout the duration of the contract.”

As well as offering informal guidance on awarding contracts, the note suggests agencies should prepare for a disorderly Brexit by deciding how to sever the UK’s access to EU information in databases.