<sod >Grant Thornton has filed a libel countersuit against the property mogul Vincent Tchenguiz, as the accountancy giant rejected allegations made in a Â£2.2bn damages claim brought by the high-profile entrepreneur and others.< eod>< sod > Two partners at Grant Thornton have filed a libel countersuit against the property mogul Vincent Tchenguiz, as the accountancy giant rejected allegations made in a Â£2.2bn damages claim brought by the high-profile entrepreneur and others.< eod>