A TORY government would consider a &ldquo;windfall&rdquo; tax on UK banks that have received state support, in an apparent sign of shadow chancellor George Osborne&rsquo;s willingness to play hardball with the City.<br /><br />One possibility for the tax, currently being discussed at the highest levels within the party, would take the shape of a new accounting rule banning state-backed banks from writing off old losses against tax.<br /><br />It is not clear whether the rule would apply just to Royal Bank of Scotland and Lloyds Banking Group &ndash; both of which are part-owned by the taxpayer &ndash; or whether it would apply to all UK lenders, which have received implicit support via the banking bailout.<br /><br />A major accounting firm contacted by City A.M. yesterday said plans of this nature were definitely &ldquo;on the agenda&rdquo; and that Labour was pondering something similar.<br /><br />Senior economic advisers to Osborne are understood to believe that banks would not threaten to leave the country if the plans became reality, because London&rsquo;s position as a leading financial centre is too important to their business models.<br /><br />The proposal &ndash; revealed in today&rsquo;s issue of the Spectator magazine &ndash; will be accompanied by measures to try and prevent banks from attempting to channel international losses through their London offices in an effort to reduce their payments to HM Revenue &amp; Customs.<br /><br />A law banning that practice could net the Treasury billions as the next government fights to erode the &pound;175bn deficit.<br /><br />The policy did not form part of Osborne&rsquo;s speech at the Tory conference, which saw him unveil plans to tackle Britain&rsquo;s debt with &pound;23bn of spending cuts.<br /><br />He outlined proposals including a public sector pay freeze in 2011, as well as a freeze on the salaries of MPs, repeating the mantra &ldquo;We are all in this together&rdquo; several times.<br /><br />In a separate interview, he said he would fight with international ratings agencies to maintain the UK&rsquo;s AAA credit rating and also suggested that the cuts he has already laid out could still be ramped up by tens of billions of pounds.<br /><br />And the shadow chancellor dropped another hint at a bank windfall tax, saying that he might take action on banks via the tax system.<br /><br />Tory MPs are also refusing to rule out a rise in VAT to 20 per cent, a move which it is estimated could raise as much as &pound;13bn to help plug the deficit.