Britain's unpredictable weather is set to continue this Bank Holiday as parts of the country bask in glorious sunshine on Sunday before temperatures plummet to near freezing in places overnight.

While temperatures could hit 20C (68F) in London and south-east England throughout the day, the mercury could fall to 1C (33.8F) in some rural areas in the south on Sunday night, forecasters said.

Most of England and Wales will enjoy clear skies and sunny spells on Sunday but heavy downpours could dampen spirits in the western half of the UK on Monday, forcing many to spend their day off indoors.

Paul Mott, forecaster with MeteoGroup, the weather division of the Press Association, said: "Much of England and Wales will enjoy sunshine today. In Scotland and Northern Ireland it will be a bit cloudier and colder at times, with one or two showers. Having said that, temperatures will still be up to 17C (62.6F) in eastern Scotland."

Mr Mott said some southern rural areas could see a sharp drop in temperatures overnight. "We could see touch of frost in rural areas in Oxfordshire and Buckinghamshire," he added. "While it may be as high as 18C in those places today, temperatures will fall to 1C or 2C overnight."

On Monday, weather conditions will be divided between eastern and western parts of the country, Mr Mott said. "Eastern parts of England will be fine and dry with sunshine and temperatures reaching 18C (64.4F)," he said.

"Further west it will be colder and breezier with outbreaks of rain. It's probably not such a good idea to be outdoors."

Up to 30mm (1.18in) of rain is predicted for south west Scotland on Monday, Mr Mott said.

The warmest weather will be in the south east of England and East Anglia, where temperatures could reach 18C (64.4F).