An Essex MP has become the third to resign from the Conservative front bench over the party's policy on Iraq.
Mr Baron is a former soldier
John Baron, who has represented Billericay since 2001, gave up his post as junior health spokesman to vote against his party in the House of Commons debate on Tuesday afternoon.
Last week Uxbridge MP and party whip John Randall resigned from the front bench, and Mid-Bedfordshire MP Jonathan Sayeed is understood to have quit his post as junior environment spokesman on Monday.
Mr Baron said during a Commons speech on Tuesday that "this moment for war is wrong" and that other measures had "not been exhausted".
Mr Baron told MPs that since the Iraqi army was a "shadow of its former self", Saddam Hussein's regime posed "no more immediate threat" than in the last 12 years.
Mr Baron was himself a captain in the Royal Regiment of Fusiliers from 1984 to 1987.
In the last vote on the issue of war, on 26 February, Mr Baron abstained.