David Cameron has raised the prospect of further sanctions against Russia as the West's relations with Vladimir Putin grew increasingly strained following the apparent shooting down of flight MH17 over Ukraine by pro-Moscow separatists.
In a sign of a hardening attitude, David Cameron said Europe and the West must "fundamentally change our approach" unless the Russian president alters course.
The comments came after a day which saw the Government adopt a tougher approach to Moscow, with Russia's ambassador summoned to the Foreign Office and Philip Hammond claiming Mr Putin was not doing enough to use his influence over the rebels in Ukraine.
The political developments came as the last two of the 10 UK victims who died were named in a Malaysia Airlines passenger list as John Allen and Andrew Hoare.
The US and EU had ratcheted up sanctions against Russia shortly before the aircraft was brought down with the loss of 298 lives, but Mr Cameron indicated that an even tougher regime might be required.
Writing in the Sunday Times he said: "We must establish the full facts of what happened. But the growing weight of evidence points to a clear conclusion: that MH17 was blown out of the sky by a surface-to-air missile fired from a rebel-held area.
"If it is the case, then we must be clear what it means: this is a direct result of Russia destabilising a sovereign state, violating its territorial integrity, backing thuggish militias, and training and arming them.
"We must turn this moment of outrage into a moment of action."
That action must go wider than just bringing those responsible to justice, he said, adding: " If president Putin does not change his approach on Ukraine, then Europe and the West must fundamentally change our approach to Russia.
"This is not about military action, plainly. But it is time to make our power, influence and resources count.
"Our economies are strong, and growing in strength. And yet we sometimes behave as if we need Russia more than Russia needs us and the access we provide to European markets, European capital, our knowledge and technological expertise.
"We don't seek a relationship of confrontation with Russia. But we must not shrink from standing up for the principles that govern conduct between independent nations in Europe, and which ultimately keep the peace on our continent."
Expressing his frustration at some of his fellow European leaders, Mr Cameron said: "For too long, there has been a reluctance on the part of too many European countries to face up to the implications of what is happening in eastern Ukraine.
"Sitting around the European Council table on Wednesday evening, I saw that reluctance at work again."
Mr Cameron demanded immediate access to the crash site, with the crime scene preserved and the remains of victims treated with "proper dignity and respect".
Moscow must also stop supplying and training the rebels, he added.
If Russia did not "use this moment to find a path out of this festering, dangerous crisis" then "we must respond robustly", Mr Cameron said.
Earlier the Prime Minister spoke by telephone to Dutch counterpart Mark Rutte, whose countrymen and women made up the majority of the passengers on the doomed Amsterdam to Kuala Lumpur flight.
They agreed that the European Union should "reconsider" its approach to Russia in light of evidence that the plane was shot down by separatists.
Foreign Secretary Mr Hammond expressed his frustration with the Kremlin after chairing a high-level meeting of officials, including from the intelligence agencies.
He said: "We're not getting enough support from the Russians, we're not seeing Russia using their influence effectively enough to get the separatists, who are in control of the site, to allow the access that we need.
"This has brought the whole international community together.
"This is not about Russia and the West, this is about the whole community demanding that the proper access is made available to this site, the victims are properly recovered and evidence is secured.
"The world's eyes will be on Russia to see if she delivers on her obligations in the next couple of hours."
A Downing Street spokeswoman said monitors from the Organisation for Security and Co-operation in Europe had been given only "limited" access to the crash site.
As well as Mr Rutte, the Prime Minister spoke to Australian premier Tony Abbott about the catastrophe and they agreed to increase pressure at the UN Security Council for investigators to access the site.
A No 10 spokeswoman said: " All three leaders are clear that president Putin needs to actively engage with the international community and use his influence on the separatists to ensure they allow access to the crash site.
"The FCO in London has called in the Russian ambassador to make these points."
Ambassador Alexander Yakovenko was urged to make sure the Russian authorities use their influence to secure access to the site for accident investigators and victim identification specialists, in a meeting with Foreign Office political director Sir Simon Gass.
In a statement the Russian Embassy said : "Ambassador Yakovenko and Sir Simon agreed that the tragedy must be investigated in an objective, open and independent manner, under the auspices of the International Civil Aviation Organisation and with the participation of other international bodies and interested countries.
"Russia and the UK believe that all parties to the conflict are to ensure access of international experts to the crash site. The Russian ambassador stressed that it is counter-productive for governments to announce their versions of the disaster, as this amounts to putting pressure on the future investigation.
"They also discussed the general prospects of a political settlement of the crisis in Ukraine.
"Mr Yakovenko pointed to the necessity of stopping the armed operation of the Kiev authorities so as to create conditions for a wide national dialogue. He expressed his regret at the recent decisions by the United States and the European Union regarding sanctions with regard to Russia which can only encourage the Ukrainian authorities to continue violence."
A team of six investigators from the Air Accidents Investigation Branch is in Ukraine, working with international counterparts on the next steps in the effort to establish what happened to MH17.
Experts from the Metropolitan Police are due to arrive in the country tomorrow to assist in the grim task of recovering, identifying and repatriating the bodies of those killed.
Malaysia Airlines identified the nationalities of 298 people who were on board the doomed flight which included 10 people from the UK, one of whom had dual UK and South African citizenship.
There were 193 from the Netherlands, 43 from Malaysia, including 15 crew and two infants, and another 27 from Australia. The dead also include 12 from Indonesia including one infant, four from Germany, four from Belgium, three from the Philippines plus a Canadian and a New Zealander.
Mr Allen was described as a "much-loved colleague" by his friends at international law firm NautaDutilh, who said they were "shocked" by his death alongside his wife and their sons.
Mr Hoare, 59, who worked in banking, died in the crash alongside his Dutch wife and their sons Friso and Jasper, who were Dutch.
His brother Hugo Hoare told the BBC: "He was a warm, funny and wonderful man whose smile and character lit up a room."
The bodies of passengers, which have been strewn across the crash site for nearly 48 hours, are finally being recovered by Ukrainian authorities.
Mr Hammond said the UK's priority is to ensure the victims are treated with dignity and respect as they are recovered from the scene.
Ukraine has accused the rebels of already removing 38 bodies and taking them to the rebel-held city of Donetsk.
Kiev also claimed Russia had helped separatists destroy evidence at the site, a charge the rebels deny.
Along with Mr Allen and Mr Hoare, the British victims included Newcastle United fans John Alder, 63, and Liam Sweeney, 28, who were travelling to New Zealand to watch the team's pre-season tour.
Also on board were Glenn Thomas, 49, a press officer at the World Health Organisation and a former BBC journalist, Loughborough University student Ben Pocock, reportedly 20, and Leeds University student Richard Mayne, 20, from Leicestershire.
Helicopter rescue pilot and father-of-two Cameron Dalziel, 43, who is understood to have been South African but was travelling on a British passport, also died along with Stephen Anderson, 44, a former RAF search and rescue co-ordinator.
Father-of-two Robert Ayley, who was originally from Guildford, Surrey, but was living in New Zealand, was also among the dead.