Andrew Boff is the Deputy Leader of the GLA Conservatives and a Member of the Council of Europe.

With Brexit now certain to happen at the end of the month, the UK is preparing for the negotiations to move onto the future relationship.

Indeed, Boris Johnson hosted the President of the European Commission, Ursula von der Leyen, in Downing Street this week, kicking off a race against time to secure a free trade deal.

With this short timeframe, the last thing we need is the prospect of a major disruption – but Croatia’s new presidency of the European Union, which began on the first of this month, could pose exactly that risk. Croatia’s presidency of the Council of the EU, its first since joining the EU in 2013, will last until 30 June 2020. It will also be crucial to the success or failure of Brexit negotiations, which is among Croatia’s top priorities during its presidency.

Negotiations over Britain’s future relations with the EU, including a free trade agreement, will begin after January 31. My worry is that Russian influence in Croatia has the potential to derail or obstruct progress towards a viable free trade deal that works for all. There have been numerous worrying developments in Croatia, especially regarding Russian encroachment.

We know that Russia would prefer a fragmented Europe that devolves into in-fighting. A successful post-Brexit free trade deal between the UK and the EU would be anathema to Russia, blocking its hopes of escalating its meddling in the internal affairs of countries across Europe.

The last few years has seen mounting evidence of Russia using its levers within Croatia to influence European affairs.

Croatia’s biggest multi-billion Euro company, Agrokor, is now partially owned by two Kremlin-backed banks, Sberbank and Vneshtorgbank, which hold a 47 percent stake in Agrokor.

Before they bailed out the ailing firm, Agrokor’s revenues accounted for some 15 percent of Croatian GDP – the same percentage the City of London represents relative to UK GDP. As such, the deal gave Putin massive indirect leverage on the Croatian economy, and on the largest firm in the former Yugoslavia.

Shortly after the bailout, Gazprom exploited the Russia-friendly political climate by signing a 10-year contract to deliver one billion cubic meters (bcm) of gas to Croatia every year, ensuring the country’s dependence on Russia.

More recently, mere days before Croatia’s ascendancy to the EU presidency, a Croatian court found the head of Hungarian energy group MOL, Zsolt Hernadi, guilty of bribing Croatia’s former Prime Minister, Ivo Sanader, to allow MOL to take control of Croatian state energy firm INA.

But two legal experts appointed as independent trial monitors in the decade-long legal battle have firmly rejected the integrity of the Croatian state prosecution and trial. Seemingly obscure, the details reveal a dangerous game at work with Putin at its centre.

Kai Ambos, a judge in the Kosovo Specialist Chambers, The Hague, and Lord David Anderson QC of Brick Court Chambers, audited the fairness of the criminal proceedings. Their detailed 182-page trial report accuses Croatian state prosecutors of “bias” in favour of Croatian “national interests”, breaching internationally-recognised fair trial standards “including violating Article 6(1) of the European Convention on Human Rights (ECHR)”, and violating the “fair trial rights” of the defendants – by, for instance, not allowing sufficient preparation time and excluding the public from key points in the trial without record in Court minutes, among many other breaches.

Such grave irregularities raise serious questions about Croatia’s fitness to lead the EU presidency, and the EU overall as a credible institution. But what is particularly concerning is the geopolitical backdrop alluded to by the report suggesting a Russian-backed covert lobbying operation to become the new strategic energy partner for Croatia (and by extension the EU).

The entire bribery story rests on the testimony of a single witness, Croatian tycoon Robert Jezic. During the trial, as the independent trial monitors report points out, his claims were called into question by oil industry consultant Imre Fazakas and Russian oil magnate Mikhail Gutseriev.

Both witnesses told the court the bribe money received by Jezic as an alleged go-between to pass on from MOL to Sanader had nothing to do with either, but instead was given to him by Gutseriev, with Fazekas’ assistance, as part of a lobbying effort for the Družba Adria project. The latter was a longstanding Russian pipeline plan to transport Russian energy to Europe.

Gutseriev testified that Jezic had “stolen” his €5 million; and Jezic admitted to the court that he used the sum to benefit his own companies and never even passed any of it to Sanader. Yet as the trial monitoring report points out, these issues were not properly investigated by Croatia’s state anti-corruption agency, nor duly considered at the trial.

In short, the verdict from this seemingly obscure trial has huge ramifications: it not only poses disturbing questions around Russia’s interference in the Croatian judiciary, but by extension about Russian influence on the Council of the EU under Croatia’s presidency.

On the one hand, we can be glad that Britain is exiting from this melodrama of escalating corruption. But it also means that to ensure a clean escape, the UK must be on its guard against efforts by Russia to derail the Brexit negotiations.

As the Prime Minister has repeatedly stated, the UK is leaving the EU, not Europe. As part of our international and moral obligations we should not be afraid to call out human rights abuses, judicial manipulation, and attacks on the rule of law, regardless of which countries are responsible for them.

We must also be vigilant towards countries that may seek to do us harm and monitor the ways in which they seek to influence our affairs.