A Downing Street spokesperson said:
The Prime Minister regrets that Baroness Warsi has decided to stand down and is grateful for the excellent work that she has done both as a Minister and in Opposition.
Our policy has always been consistently clear - the situation in Gaza is intolerable and we've urged both sides to agree to an immediate and unconditional ceasefire.
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Labour strongholds tended to remain so - apart from a major loss for the party in Dudley.
Labour suffered a "terrible" defeat in Rhondda but has already won 16 Welsh Assembly seats as it looks to record a fifth term in office.
UKIP have made further gains in the local elections in the Anglia region and the Conservatives have won back control in Peterborough.