DUSK started falling on Sir Keir Starmer’s premiership today as his government was engulfed by an extraordinary outburst of right-on-right political brawling.The Prime Minister was forced to declare “full confidence” in Health Secretary Wes Streeting in the Commons after Downing Street aides launched a briefing war against the leading Blairite.Mr Streeting denied that he was plotting to overthrow Sir Keir, following allegations by No 10 that he was plotting to force out the beleaguered and blundering PM.