More torrential showers are expected to sweep across Britain on Wednesday, bringing the risk of flooding to areas that have so far escaped the deluge.

The Met Office said parts of south-west England were likely to bear the brunt of the next wave of heavy showers, with up to 60mm (more than 2in) of rain, about the average for all of June, threatening to fall in Cornwall.

Further effects of the recent weather were predicted for west Wales, still mopping up after the “once-in-a-lifetime” floods that wreaked havoc over the weekend. Up to 30mm of rain could fall on the saturated ground.

And scientists were investigating whether the rain could have swept potentially harmful metals, such as lead and zinc, from old mines into farmer’s fields and close to villages and towns.

Surveyors were checking roads, bridges and dams that might have been damaged in the downpour and the Welsh government promised to treat sympathetically any appeals from local authorities to help with rebuilding.

The Met Office issued a severe weather warning for Wales and for the south-west of England. Andy Page, the chief forecaster, said: “Due to the nature of showers some areas will miss them altogether, but where they do occur large amounts of rainfall are possible in a short space of time which has the potential to cause flooding.”

David Bunt, the Environment Agency‘s emergency planning manager for the south-west region, said: “We are keeping a close watch on river levels, as the weekend’s heavy rain has left many areas more vulnerable to flooding.

“Environment Agency teams have been working round the clock, with other emergency responders, checking flood defences, clearing blockages, monitoring river levels and issuing flood alerts or flood warnings where necessary.”

By Tuesday night more than 30 flood alerts (signalling flooding a possibility) were in place in all areas of England except the north-west. Four of the more serious flood warnings had been issued, two in the south-east, two in Bedfordshire.

One of the worst affected areas in England was West Sussex, where firefighters had to use boats to reach about 250 homes cut off in Elmer, near Bognor Regis. More than 30 people were rescued from holiday parks in Sussex.

People who had been driven out of their homes were sheltered in rest centres and in bed and breakfast accommodation.

Some schools were closed and A-roads shut. There were lengthy delays on the M3 in Hampshire after two lanes were closed because of flooding.

It was not only people who found themselves in danger. The RSPCA rescued a herd of 21 cows marooned on a patch of high ground when the river Arun broke its banks in West Sussex.

In the Welsh assembly, Carl Sargeant, minister for local government and communities, said the devastation in west Wales had been astonishing. He said that at one point a device to measure flow recorded 250 tonnes of water passing every second.

Sargeant said he was shocked at reports of some insurance company representatives telling people to put furniture contaminated with raw sewage back into their homes, and he said officials would be talking with the industry to make sure people got the right advice.

Assembly members representing some of the areas that were affected expressed concern that tourism in west and mid Wales would be harmed by the pictures of devastation being transmitted around the world. Sergeant emphasised that the flooding was very localised and Wales was “open for business”.