Residents and businesses in Wales are bracing for more flooding resulting from bad weather as many people continue to mop up the devastation of last month’s storms.

An amber weather warning has been issued by the Met Office for parts of mid- and north Wales, where up to 100mm of rainfall could fall over Monday and Tuesday.

The Met Office issued a “potential threat to life” warning on Monday to areas including Builth Wells and Newtown in mid-Wales, warning of possible power cuts, fast-flowing flood water and damage to homes and businesses. The amber warning is in place from 6pm on Monday to 10am on Tuesday.

The Met Office said between 20 and 40mm of rain was likely to fall widely, with many upland areas expected to see between 50 to 70mm of rainfall. Some hills and mountains may have about 100mm of rain. Some communities could be cut off and delays to train and bus services are likely.

Natural Resources Wales issued flood alerts for rivers in south Wales including the Usk and the Wye and further north for the Severn and some of its tributaries.

A yellow weather warning, a grade below amber, is in place for areas of south, west, mid- and north Wales, including areas recently flooded during Storm Dennis. The alert, in place from 3pm on Monday until 12pm on Tuesday, also warns that homes and businesses could be flooded.

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The Met Office meteorologist Greg Dewhurst said: “We will see rain spread in from the west. Then we will see heavy rain right through the rest of Monday, overnight and into Tuesday morning. The ground is already saturated and with all the rainfall we have had over recent weeks, it is likely to lead to further flooding in places.”

A yellow warning was also in place for parts of the north of England and the West and East Midlands. While there are no weather warnings in place for the later half of the week, there will be widespread showers, meaning flood-hit areas will have little respite.

Play Video 0:19 Boris Johnson heckled as a 'traitor' while visiting flood-hit Worcestershire – video

Boris Johnson was heckled on Sunday when he visited the town of Bewdley in Worcestershire on the Severn, which in February had some of the worst flooding in the country.

The prime minister has been heavily criticised for not visiting flood-hit communities during the crisis. Some onlookers shouted “traitor” as Johnson inspected the flood defences. He said during the visit it was “too easy” for a PM to “come to a place in the middle of an emergency” but that it was “not so easy, frankly, for the emergency services”.

He added: “What they have to do is then break off and gold command has to find somewhere to brief you, everybody has to gather. They’re diverting from their work for hours and hours.

“What I’ve been doing since the flooding began is coordinating the national response, but also looking at what we can do in the next months and years to ensure this country really is ready to cope with the impacts of flooding.”