The organisers of the London Marathon say they "fully expect" it to go ahead as planned on Sunday, although "security will be reviewed", after two explosions hit the Boston Marathon yesterday, although "security will be reviewed."
Vale of Glamorgan MP Alun Cairns is among the Welsh runners taking part, and has urged others to "turn out in confidence."
As a runner in Sunday's #LondonMarathon I hope all athletes & spectators turn out in confidence & defy the terrible acts in Boston
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Many places will start dry, but rain in the southeast will spread to most for a time overnight.
The family of Isaac Nash who went missing after being swept out to sea last summer have presented a cheque for £10,000 to the RNLI.
There is likely to be a good deal of cloud around today, thickest in the southeast, where outbreaks of rain are possible at times.