Letting the Scottish Nationalists dictate the direction of the UK government would be like getting King Herod to 'run a baby farm', Boris Johnson warned today in an escalation of Tory attacks on the SNP. The Tory London Mayor warned against allowing Nicola Sturgeon's SNP to dominate the government of the UK, 'an entity that they are sworn to destroy'. He likened it to 'asking a fox to look after the henhouse or a temperance campaigner to run a brewery'. Tory London Mayor Boris Johnson warned against allowing Nicola Sturgeon's SNP to dominate the government of the UK 'an entity that they are sworn to destroy' Ms Sturgeon launched her SNP manifesto today, boasting that she can 'lead the UK' with polices on British foreign policy, benefits, energy bills and English university tuition fees. The SNP leader vowed to use a surge in support for her party to dictate the direction of the UK government, calling for an end to austerity, rising benefits payments and the abolition of Trident as the price Ed Miliband would have to pay for propping up a weak Labour government. Ms Sturgeon set out a 'programme for delivery on a UK-wide basis', raising the prospect of Scottish nationalist MPs calling the shots on policies which apply only in England, Wales and Northern Ireland. Polls suggest up to half of Scots are planning to vote SNP, handing the party dozens of seats and leaving Labour's Ed Miliband unable to secure a majority. The SNP has claimed that it will be 'entitled to vote against any bit of legislation' and 'any bit of spending' it does not agree with. Mr Johnson, who is expected to play a more high profile role in the Tory campaign from this week, issued a blunt warning about allowing an anti-Union party to dictate policy in Westminster. 'You wouldn't get Herod to run a baby farm, would you?,' he wrote in the Daily Telegraph. 'It would not normally occur to you to interview a convicted jewel thief for the post of custodian of the Tower of London. 'You would not dream of asking a fox to look after the henhouse or a temperance campaigner to run a brewery or Attila the Hun to work as a doorkeeper for the Roman senate. 'Any such course of action would be totally nuts. So can someone tell me why in the name of all that is holy there are some apparently rational people who are even contemplating the elevation of the Scottish Nationalist Party to a position of effective dominance in the government of the United Kingdom - an entity that they are sworn to destroy?' He said the SNP want to 'end Britain, to decapitate Britannia' but Mr Miliband has no chance of entering Number 10 without their support. Nicola Sturgeon today demanded an end to austerity as the price for propping up a Labour government in what was quickly dubbed a £140billion 'ransom note' for Britain . The SNP want higher taxes, to scrap Trident and end efforts to reform the welfare system, Mr Johnson warned. Mr Miliband will be left 'sitting in the driving seat, pretending to be steering the car - but all the time he will have clever Nicola next to him, whispering in his ear, and perpetually yanking the steering wheel to the Left'. Speaking at her manifesto launch, Ms Sturgeon said she had not 'heard the comments of Boris Johnson directly'. But speaking at the SNP manifesto launch, she said: 'If he did say that, then that is an entirely offensive comment, and I think it will be treated as that not just by people in Scotland but across the UK, who, in my experience, ordinary people the length and breadth of the UK do not see Scotland that way at all and do not see the SNP in that way at all.' However, the warning was echoed by David Cameron today, in a speech setting out the risks to England, Wales and Northern Ireland if the Scottish Nationalists are calling the shots. The Prime Minister yesterday suggested key services like roads and hospitals in the rest of the UK would suffer as a price of SNP support. ''This would be the first time on our history that a group of nationalists from one part of our country would be involved in altering the direction of the government of our country. I think that is a frightening prospect,' he told BBC One's Andrew Marr show. 'People thinking in their own constituencies, is that bypass going to be built, will my hospital get the money it needs? Frankly this is a group of people that wouldn't care about what happened in the rest of the country. 'The rest of the United Kingdom – England, Wales, Northern Ireland, wouldn't get a look-in. 'That is the prospect we face if we don't get the majority Conservative government that is in our reach.'
London Mayor warns the SNP want to 'end Britain, to decapitate Britannia' Says Scottish Nationalists want higher taxes and welfare payments . David Cameron warns England, Wales and Northern Ireland would suffer . Nicola Sturgeon launches manifesto with vow to 'lead' the United Kingdom .