The Environment Agency has apologised to Oxfordshire residents for failing to issue a flood warning until six hours after they were under water.
Among the flooded were seven properties in the Wendlebury area and another three in Steventon near Abingdon. It happened when a third of a month's rainfall (33mm) fell in one night last week.
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The expansion of the probe came as Jeremy Corbyn declared Carillion's demise a "watershed moment" that should end "rip-off privatisation".
Tuesday afternoon's weather for the west of the region
Tuesday afternoon's weather for the east of the region