Delays of up to 45 minutes on First Capital Connect between Bedford and Brighton, and between Luton and Sutton due to overhead line problems at Elstree and Borehamwood.
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Southampton's marathon runners worked up a sweat as temperatures touched 20c but there was help on hand to keep them cool.
The Duchess of Cambridge has been driven to St Mary's Hospital in London in the "early stages of labour", Kensington Palace has said.
The Duchess of Cambridge has been on maternity leave since the week before Easter.