In a field at a secret location, dozens of armed Ukrainian soldiers are running through billowing smoke and trying to escape the attention of drones buzzing overhead.

The scene is an adrenalin-fuelled theatre of the war – but, on this occasion, it is manufactured.

The field is in East Anglia, not Kursk, and the drones are dropping water balloons, not explosives. Rubber bullets are fired instead of the real thing and the day will end without a single casualty.

This is how Britain prepares Ukrainian troops for the front line – and has been doing so since a formal training scheme was introduced in June 2022.

But more than 1,000 days into the conflict, the nature of the battlefield preparations has changed significantly – along with the mindset of those benefiting from the experience.

Drones and unmanned aerial vehicles (UAVs), for example, are currently taking centre stage ahead of deployment in Ukraine, which one senior British commander describes as a “laboratory for the evolving character of war in a conflict”.

The Ukrainian recruits, who have travelled to the UK for up to 10 weeks, face a far harder task than those who first embarked on the scheme two years ago.

Then, victory seemed possible; now, a total defeat of Russia seems far more difficult to envisage.