BORIS Johnson has told the UK to prepare for a "long war” in Ukraine.

The Prime Minister, who made a surprise visit to Kyiv on Friday, warned that “no nation anywhere would be safe” if Russia was successful in its bid to secure territory, because “every dictator would feel emboldened to pursue their own ambitions by force”.

Writing in The Times, Mr Johnson said: “I am afraid that we need to steel ourselves for a long war, as Putin resorts to a campaign of attrition, trying to grind down Ukraine by sheer brutality.

“The UK and our friends must respond by ensuring that Ukraine has the strategic endurance to survive and eventually prevail.”

“Everything will depend on whether Ukraine can strengthen its ability to defend its soil faster than Russia can renew its capacity to attack,” he added.

“Our task is to enlist time on Ukraine’s side.”

The first measure on the Prime Minister’s four-stop plan is to provide “weapons, equipment, ammunition and training more rapidly than the invader”.

He said the UK is aiming to work with allies in training up to 10,000 soldiers every 120 days to support Ukraine.

Mr Johnson describes step two as providing “constant funding and technical help,” while the third is developing alternative overland routes to overcome the Russian blockade on ports including at the southern city of Odesa.

Mr Johnson said 25 million tonnes of corn and wheat is being “held hostage” by Russia – and the fourth step of the plan is to free these supplies.

This can be achieved by supporting the UN’s efforts to negotiate an exports corridor via the sea, according to the Prime Minister.

Mr Johnson met President Volodymyr Zelensky in Kyiv on Friday in an unannounced move.

Speaking with reporters at RAF Brize Norton in Oxfordshire on his return, he stressed the need to demonstrate support for Ukraine when its people were “suffering terribly” particularly in the Donbas.

In his talks with Mr Zelensky, Mr Johnson said Britain would be prepared to train tens of thousands of Ukrainian troops.

He said it was important to prevent the Russians “freezing” the conflict so they could consolidate their gains before mounting another attack, and that Ukrainians should be supported to regain territory lost this year.

However, he stopped short of calling for the recovery of all the lands Ukraine had lost since 2014 – including Crimea – something Foreign Secretary Liz Truss has previously called for.

Mr Johnson’s visit was warmly welcomed by the Ukrainians, with television footage of Mr Zelensky showing the Prime Minister the wreckage of burned out Russian tanks and other vehicles on display in Kyiv’s St Michael’s Square.

Meanwhile, the new head of the Army has said British troops must prepare “to fight in Europe once again” as the conflict in Ukraine continues.

General Sir Patrick Sanders took over from General Sir Mark Carleton Smith on Monday and wrote to his charges about the challenges they face.

“There is now a burning imperative to forge an Army capable of fighting alongside our allies and defeating Russia in battle,” Sir Patrick said.

“We are the generation that must prepare the Army to fight in Europe once again,” he added.