The Duke of Edinburgh faces a fourth day in hospital as he recuperates following exploratory abdominal surgery.
Philip, who is 92 tomorrow, was admitted to the London Clinic on Thursday following a garden party at Buckingham Palace and underwent the procedure on Friday.
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The ComRes survey for ITV News and LBC showed the Labour candidate increasing his overall lead over Conservative rival Zac Goldsmith.
The latest poll for ITV London and LBC shows Sadiq Khan leads Zac Goldsmith by 45% to 36% on first preference votes.
Corbyn was unveiling a poster less than a mile away as Khan gave his final campaign speech to party supporters in London.