The United States and Britain were last night still locked on a collision course with President Saddam Hussein of Iraq as Russian mediators struggled to win concessions to avert a military outcome to the crisis over United Nations weapons inspections.After a confusing flurry of statements, Baghdad insisted it had not agreed with Russia's special envoy, Mr Viktor Posuvalyuk, in Baghdad to allow UN inspectors into off-limits presidential palaces, although the reported offer had already met a hostile reception in Washington and London.Iraq denied Russian claims that Mr Saddam was willing to meet the chief UN arms inspector, Mr Richard Butler, to discuss the stand-off that has brought threats of "substantial" US-led military action."The discussions are going on and they are quite, quite detailed," said Mr Riyad al-Qaisi, an Iraqi deputy Foreign Minister.Russia was clearly eager for success. President Yeltsin telephoned President Clinton with news of the offer, but reactions were swift and negative. Mr Bill Richardson, the US ambassador to the UN, said bluntly: "This so-called compromise is unacceptable."A spokesman for the British Prime Minister, Mr Tony Blair, was also dismissive: "We need some convincing that this is any more than game-playing," he said. "I do not think it much changes where we are." The British Foreign Secretary, Mr Robin Cook, expected to consult Arab leaders later this week, told the House of Commons: "Although we are pursuing a diplomatic solution, we have not, nor will we, rule out the use of force."Russia had reported that Mr Saddam was ready to allow UN inspectors to visit eight previously closed "presidential" sites as representatives of their governments and to be accompanied by diplomats from the five permanent members of the UN Security Council.But the grounds adjoining the sites would be excluded from inspections, rendering the offer meaningless in the light of reports that great efforts have been made to conceal suspected chemical and biological weapons programmes.Since last year Mr Saddam has refused to allow the UN to check some 60 sites on grounds of national sovereignty. The UN is insisting on "full and unconditional access".Yesterday's developments came after Mr Yeltsin warned that military action was "fraught with unpredictable consequences and would cause big casualties among civilians".Israel began preparing its defences against the threat of an Iraqi attack by setting up USmade Patriot missiles near the Dimona nuclear reactor in the Negev desert.The US Secretary of State, Ms Madeleine Albright, spent the day in Saudi Arabia as part of a Middle East and European tour to drum up support for air strikes. She said that Washington and Riyadh had agreed that "if diplomacy fails to achieve a solution, Saddam Hussein will be responsible for the grave consequences".Apart from Kuwait, only Britain has thrown its weight unconditionally behind Washington. Six Sea Harrier jump jets left their base at Yeovilton to join the carrier Illustrious in the Mediterranean, en route to replace Invincible in the Gulf.Iraq will invite the US Congress to send a delegation to visit Saddam Hussein's palaces which the Iraqis have placed off limits to UN weapons inspectors, Baghdad's UN Ambassador said early today. Ambassador Nizar Hamdoon said the invitation would be faxed last night to the US House of Representatives Speaker Newt Gingrich, inviting him to send a congressional delegation to Iraq.Mr Hamdoon said the invitation would include any weapons experts the congressmen would like to bring. "We want to allow them to make sure for themselves there are no prohibited items in those sites," he said. Israelis test Patriot missile interceptors as fears of Iraqi strikes intensify; US has policy allowing nuclear attack on Iraq: page 11