Vladimir Putin’s strategy of waiting for Donald Trump to return to the White House is “another Kremlin miscalculation”, a former secretary-general of Nato has said.

Lord Robertson of Port Ellen, also a former UK defence secretary, argued that, despite his Russia-friendly rhetoric, Mr Trump actually bolstered American defences and Nato contributions as US president.

The Labour peer recalled Republican members of US congress also insisting that Mr Putin’s plan is flawed during a visit to the UK.

“When he was in office, in spite of his rhetoric, President Trump sent missiles to Poland, increased funding to Nato and robustly increased the power of his own military.

Lord Robertson told the House of Lords: “Now at the moment, with no real Russian progress, Putin, it would appear, can only wait it out until Donald Trump gets elected, who he hopes will do some grubby deal to end the war.

“But even that strategy, if that is what it can be called, is incorrect.

“Republican members of the United States congress were here with the Marshall Fund and they were very keen to articulate that that strategy is flawed.

“When he was in office, and in spite of his rhetoric, President Trump sent missiles to Poland, increased funding to Nato and robustly increased the power of his own military.

“And, therefore, it begins to look like yet another Kremlin miscalculation.”

By contrast, a former top diplomat has argued that tens of billions of pounds’ worth of support for Ukraine will be at risk if Donald Trump is elected.

Independent crossbench peer Lord McDonald of Salford, a former ambassador who headed the Foreign Office from 2015 to 2020, said: “The United States has provided at least 50% of the military capability that the Ukrainians have been using.

“Donald Trump will change American policy, no matter that groups of American politicians agree with their President (Joe Biden), the US constitution makes the President of the United States the key player in foreign and defence policy.

“So if Donald Trump becomes president of the United States, we face the prospect of the disappearance of the majority of military persistence that Ukraine needs to continue and to win this fight.

“So the question for us and the rest of the West is: are we prepared to make up the huge difference? This is tens of billions of pounds and these are necessary for the fight to continue.”

Former head of the Armed Forces, Lord Stirrup, argued that Western Europe should not rely too much on the US and that, with the proper investment, could outmatch Russia, even without its ally across the Atlantic.

The independent crossbench peer and former RAF commander said: “If the outcome in Ukraine is as critical as the Government – rightly in my view – claims, then the countries of Western Europe simply cannot allow their safety and security to be subject to the vagaries of American politics.

“They need to increase defence expenditure significantly, expand defence industrial capacity and coordinate their efforts, both to support Ukraine and to strengthen Nato more widely.

“Together, the UK, France, Germany, Italy, Poland and all the other countries within Nato have more than enough economic and industrial muscle to overmatch Russia, even with the latter on a draconian war footing.

“What is required is the will to do it – and that is not yet evident. The UK should be offering a greater lead in this regard – we have to match our grand words with decisive and sustained actions, backed with the appropriate resources.”

Tory peer Lord Camoys used his maiden speech to urge the Government to keep the US in the fight, which he argued involves Europe showing its own commitment through defence spending.

He said: “Western support must be non-negotiable, as others have said, it saddens me that maintaining American support for Ukraine should even be something that we are worrying about.

“We should use all our diplomatic skills to keep America on-side and part of that probably involves Europe being prepared to pay more for our own defence.”

Former Nato chief Lord Robertson added that, from his personal experience working with Mr Putin, his inner circle is more fragile than people may think, citing the march on Moscow by Yevgeny Prigozhin and his Wagner Group in June last year.

Whilst the uprising was swiftly quashed, it gave Russians – and the rest of the world – a glimpse into the internal conflicts in Mr Putin’s camp, and saw Prigozhin dismiss the President’s claim that the invasion of Ukraine was for “denazification”.

Lord Robertson told peers: “In my personal view, and I dealt with Putin in better times, there is a weakness inside the secret enclave in the walls of the Moscow Kremlin.

“From the outside we, and indeed the Russian people too, cannot know how fragile is the morale in the circle around Putin.

“But from the Prigozhin incident, here was a man invented, organised by, used by Putin, brutally exposing the truth of this disaster.

“And there we got a glimpse of the unseen tensions of the ruling elite in Russia.

“And what we saw in Prigozhin’s march on Moscow was the revelation of a serious weakness, a chink in the armour of a gambling authoritarian.

“By continuing to build our supplies to Kyiv, by maintaining Western unity and by giving the strongest possible message of our continuing resolve, the man in the Kremlin may yet see that there is a way out for him and this Russian-made, Putin-made disaster.”