Russian 'invasion', plea to Boris and Susanna Reid in papers
Reports of Russian forces on the ground in Crimea has moved the political crisis in Ukraine back on to the front pages, with many describing the situation as an "invasion".
As the United States expresses "deep" concerns, the Guardian is among the papers to suggest "Russia and the West are on a collision course".
Writing in the paper, historian Orlando Figes says Russian President Vladimir Putin must show "restraint" and not be tempted to follow Tsar Nicholas I's footsteps into the peninsula in the 19th Century.
"Memories of the Crimean war continue to stir profound feelings of Russian pride and resentment towards the west. Although it ended in defeat, the war has always been presented by the Russians as a moral victory," he says.
For the Times, "Western weakness has encouraged" President Putin to believe he can dictate the pace of change in eastern Europe.
Europe and Nato is facing the "most serious security emergency since Russia's invasion of northern Georgia in 2008, and arguably since the end of the Cold War," it says in an editorial.
While a new status for Crimea following a May referendum "should not be ruled out" the West must "act with new-found clarity and resolve" and be prepared to use economic sanctions if Ukraine's borders are violated, the Times adds.
An editorial in the Daily Mail says the "West has been left looking frighteningly impotent" over its approach.
"Putin is acutely aware there is no desire in Washington... or elsewhere to get involved in a military confrontation," it says.
"He also knows only too well that he could inflict catastrophic damage on the economy of Britain and other EU nations simply by turning off the gas taps."
President Putin is likely to play a "waiting game", suggests John Kampfner in the Daily Telegraph.
The paper's former Moscow bureau chief adds: "The best, and possibly only, hope for Ukraine to emerge relatively unscathed (with or without control of the Crimean peninsula) is for the establishment of a solid and uncorrupt administration in Kiev."
Message to Boris
In another story related to Ukraine, the Independent reports that hundreds of millions of pounds of state assets believed to have been owned or used by the ousted President Viktor Yanukovych and his circle are alleged to have been funnelled through London front companies.
The paper says the news will increase pressure on the UK to follow the example of other countries and freeze assets.
London Mayor Boris Johnson is being urged by allies of David Cameron to stand as a Conservative candidate at the next election, the Times reports on its front page.
Chancellor George Osborne is said to have delivered personally the message to "settle once and for all questions over his loyalty" and so he can demonstrate his willingness to go "all out" for the prime minister.
The paper adds that an alternative plan is to offer him the chairmanship of the party, a move that would have the advantage of deploying one of the few politicians able to reach beyond Tory heartlands.
Millions of patients wait as long as three weeks to see their GP, a survey commissioned by the Daily Mail suggests. Only one in three manages to secure a same-day appointment, despite government promises to make these routinely available, the poll of more than 11,000 people says.
It reports that leading GPs say the figures reflect their struggle to meet the demands of a growing population with ever larger numbers of pensioners.
The Guardian highlights a study by the Campaign for Fairer Gambling which indicates more than £13bn was spent on high-stakes roulette machines by the poorest quarter of England's population last year.
In an editorial the paper calls for a reduction in the amount that can be spent on the terminals per minute. It says the "allure of these machines lies beyond the bounds of rationality" but accepts the "odds of nudging people back to their senses are long gone".
'Painful to watch'
A week which saw both David Cameron's attempts to win over the German chancellor for his plans to reform the European Union and UKIP's spring conference provokes comment.
The Guardian does not agree with UKIP leader Nigel Farage's assessment that Britain faces a "migration-driven crisis".
"Pulling up the drawbridge in the face of global economic change and the digital era, the course implied by UKIP, is simply not possible," it says in an editorial.
"Only a fool would make the mistake of not taking Mr Farage and UKIP seriously. But their goal is to embarrass the other parties, not to change the world."
"The simplicity of the UKIP leader's message obviates any need for subtlety or nuance".
It concludes that the prime minister's ability to stop UKIP triumphing in the European election does not look any greater at the end of the week than it did at the start.
For the Independent it is "painful to watch yet another British Conservative leader be tortured over Europe. Once upon a time, Mr Cameron gave his own party the sound advice that the best way to deal with Europe was simply to stop going on about it. He was right."
But it sees potential problems for Mr Cameron at the general election as he will "never be able to outflank Nigel Farage on the Eurosceptic wing of British politics".
Saving Private Ryan's grave
The Sun is among the papers to report that BBC presenter Susanna Reid's split with her long-term partner Dominic Cotton - confirmed by her agent on Friday - "scuppered" her "big unveiling" by ITV as its new breakfast show host.
The grave of a World War One soldier - Private Francis Ryan - also attracts attention.
Pte Ryan - who shares his title with the US hero of Steven Spielberg's 1998 World War Two movie - was buried at the military cemetery in Pembroke Dock after his death in 1915.
The Ministry of Defence has failed to find a living relative of Private Ryan, from Longford, Ireland, who served in the 3rd Battalion, King's Liverpool Regiment. But work is now under way to fill in the 20ft crater to prevent the headstone from falling in.
Finally, the Queen is pictured on a rare lunch visit to the prime minister's official country home Chequers.
It was only the monarch's third visit of her reign to the grace-and-favour residence in Buckinghamshire, and she and Prince Philip dined on lamb and bread and butter pudding, says the Daily Telegraph.
Mr Cameron has weekly audiences with the Queen and the Times notes Number 10's explanation that he arranged the invite after being inspired by seeing archive photographs of her previous visits so her could "host her for a change".
Daily Telegraph sketchwriter Michael Deacon reckons her last visit in 1970 was "probably a little more exciting", with US President Richard Nixon among the other guests and hundreds of Vietnam war protesters gathered at the entrance.
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