* Trump calls long-awaited stimulus bill “a disgrace” * S&P 500 futures down 0.5%, European futures fall * Virus mutation worries weigh on commods, boost dollar SINGAPORE/NEW YORK, Dec 23 (Reuters) - U.S. stock futures fell, commodities slipped and Treasuries edged higher on Wednesday after Donald Trump threw a last-minute spanner in to pandemic relief plans by threatening not to sign a long-awaited stimulus bill in to law. S&P 500 futures were down half a percent by mid-morning in Asia and European and British equity futures fell by the same margin as the news offset hints of progress toward a British trade deal with Europe. In a video posted on Twitter, Trump said the bill - the result of months of wrangling in Congress - was “a disgrace” with too much foreign spending, adding he wanted to increase “ridiculously low” $600 checks for individuals to $2000. “Really ... you got to be kidding,” said Andrew Brenner, head of international fixed income at NatAlliance in a note emailed after Trump’s message. “Personally we think the President will sign the bill at the last possible moment ... but the true reality star will wait until the end,” he said. “Bond markets close 2 p.m. Thursday while stocks close at 1 p.m. - it may go down to the last moment.” Ten-year U.S. Treasury futures rose two ticks and the yield on U.S. 10-year government bonds fell one basis point in Asia after Trump’s tweet. It also soured sentiment which had caught a boost after ITV’s political editor said in a late-night tweet that separate sources had raised the possibility of Britain and the European Union striking a trade deal on Wednesday. Holiday-thinned markets are also jittery about a highly contagious new coronavirus strain, which has given support to the safe-haven U.S. dollar and yen and dragged on the prices of growth-sensitive commodities from oil to iron ore and copper. France will re-open borders to Britain on Wednesday, but much of the world has sealed it off after a significantly more transmissible mutated coronavirus variant was discovered spreading swiftly across southern England. Scientists say there is no evidence that vaccines currently being deployed in Britain will not protect against this variant, but the possibility has begun to haunt traders. “The worry right now is whether the vaccine is less effective,” said Bank of Singapore currency analyst Moh Siong Sim. “All these unknowns are keeping markets edgy, especially when they have made quite a bit for the year from the rally. People are keen to say let’s take some money off the table.” The U.S. dollar index rose 0.1% as the greenback generally hung on to small but broad overnight gains. The Australian dollar edged higher to $0.7540 and most other majors were pretty close to flat, with the euro at $1.2171 and sterling at $1.3390. Asian stocks steadied, with MSCI’s broadest index of Asia-Pacific shares outside Japan up 0.1% after three days of declines. Japan’s Nikkei rose 0.1%, although gains were concentrated in healthcare and technology stocks. Both indexes are up more than 60% from March lows. Oil prices fell to test lows made during a sharp selloff on Monday, with Brent crude futures last down 1.5% at $49.35 a barrel and U.S. crude futures down 1.5% at $46.34. (Reporting by Tom Westbrook in Singapore and Megan Davies John McCrank in New York; Editing by Sam Holmes and Richard Pullin)