With rivers bursting their banks and groundwater brimming at the surface, the additional rainwater will put additional pressure on the underground sewers which are already full.
The firm, which operates more than 67,000 miles of sewers, has been struggling in some areas to cope with the additional water filling up its pipes.
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Holly has the early forecast for the east of the region.
Holly has the forecast for the west of the region.
More than 100 firefighters are tackling thatch fire at a Hampshire hotel.