Europe must prepare for a hard winter if it is going to keep up the economic pressure on Russia over its illegal invasion of Ukraine, the UK national security adviser has warned.

In a bleak forecast, Jonathan Powell said the continent’s people must continue to ‘swallow’ the impact of sanctions on Moscow, adding that now was not the time for its leaders to take their ‘foot off the gas’.

His rare public comments – made to an audience of Ukrainian leaders and international backers in Kyiv – came as Russia steps up attacks on Ukraine infrastructure and frontline cities.

Meanwhile as Europe prepares for its fifth winter since setting out to reduce its dependence on Russian oil and gas, experts have warned that Britain could face a winter of discontent as fears grow of a 'triple whammy' of rises to energy bills, interest rates and taxes.

At the same time, a defiant Vladimir Putin continues to insist Ukraine will ‘crumble’.

New jet-powered drones are inflicting new misery on Ukraine’s long-suffering citizens, just as his troops threaten its fortress cities in the eastern Donbas.

But saying there were ‘strong reasons for optimism’ amid the continuing carnage, Mr Powell, who helped negotiate the Good Friday Agreement in Northern Ireland, insisted now was not the time to ask Ukraine to give up territory in exchange for peace.

Instead, he told his audience that far from being a ‘problem’, talk of Russian escalation was a ‘sign of success’ as it showed Mr Putin was feeling the pressure, the BBC reported.

Mr Powell was speaking at the Yalta European Strategy forum, which heard Russian attacks are expected to cost Ukraine £7.4billion this year alone.

He told delegates that Ukraine had ‘already won’ the war, saying Mr Putin had failed in his bid to seize the whole country.

And whatever territory it loses, it would still remain ‘a free Ukraine in Europe’ able to choose its own path.

Therefore now was not the time for EU countries to succumb to the temptation to soften the painful increases in energy prices by turning to sanctioned Russian gas, he said.

Warning of the need to ‘keep the pressure up’, he added: ‘It will require some real hardship and difficulties on our parts.

‘But we will have to swallow that and we have to keep the economic, military, political and diplomatic support going for Ukraine.’

And with Ukraine continuing to target Russian infrastructure with its own long-range drone strikes, Mr Powell said President Trump was no longer ‘leaning in the direction of Putin’ over his previous land-for-peace proposal.

Instead, the strategy must be to put sufficient pressure on Mr Putin to bring him to the negotiating table.

British consumers continue to suffer the impact of the war in Ukraine, with rising oil prices having a knock-on effect on energy prices.

At the same time, the Bank of England is hinting at a rise in interest rates, while Andy Burnham and Chancellor John Healey have been refusing to rule out more tax hikes in the Budget next month.