His agent has told ITV News the 72-year-old died from a short illness. He was surrounded by his family at a hospice in Rotherham in South Yorkshire.
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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.
Labour have held Sunderland, Newcastle, Hartlepool and South Tyneside - but UKIP and the Lib Dems make some gains