An advice centre for those affected by floods in Nottingham will be opened at Southwell Town Hall, The Burgage, Southwell, later today.
The A612 remains closed between Southwell and Thurgaton to enable urgent clean-up operations to take place.
A month's rain fell in just a few hours in some areas yesterday.
Pershore in Worcestershire recorded 56mm (2.2 inches) of rain in a three-hour period this morning, more than the area's 50mm average total for the whole of July, the Met Office said.
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.