Temperatures are set to soar this weekend and into early next week as the Met Office warned of a heatwave.

Saturday is expected to be sunny with showers heaviest in parts of Scotland, northern England, Wales and the Midlands and the possibility of some isolated thunder.

Bright spells are forecast for Sunday, in what the weather service described as a “fine and dry day for many”, with temperatures expected to reach highs of 27C in the South and 25C in the North East.

Conditions are looking increasingly warm into Monday and early next week, with the Met Office confirming that some places may reach “heatwave criteria”.

Heatwave criteria is when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold which varies by county.

However, it is uncertain how long the warmer weather will last, with a possible breakdown coming next week.

Deputy chief meteorologist at the Met Office David Hayter said: “As we go through the weekend, the jet stream will weaken to the west of the UK, generating an area of high pressure that will slowly move in across the UK.

“High pressure means the air is sinking from higher in the atmosphere and that brings drier, settled and sunnier weather.

“Temperatures will rise too, becoming widely above average. We could see maxima of 27C in the South and 25C in the North East by Sunday.

“There’s a bit more in the way of patchy cloud in Northern Ireland, south and west Scotland and the Northern Isles, so temperatures will be lower there.”

Earlier in the week, Met Office forecaster Greg Dewhurst warned that despite the warm weather, water temperatures could be much lower.

Mr Dewhurst told the PA news agency: “At this time of year people head to the beach when the weather’s warm or off to local lakes and rivers.

“Be mindful that at this time of year the water’s still pretty cold, around 16, 17, 18C, it’s not like in the Mediterranean where it’s much warmer.”

Tom Morgan, meteorologist at the Met Office, said the hot weather is due to the fact that “days are longer at this time of year, we’re only one month past the summer solstice and when it’s a sunny day, temperatures build because the land retains more heat than it loses by night”.

Mr Morgan said: “Even with no change in wind direction, we’re not drawing up weather from the south but it’s more to do with the fact that the sun is heating the ground during the day, creating a net increase in heat because the nights are shorter than days. The net balance of solar radiation increases.

“Although there’s no plume of hot air from the south initially in this warm spell, by around Wednesday next week we could start to tap into some more humid air from France, so it could start to feel more humid.

“Temperatures will be above average, but if you do live in the South East we could see it turn hot and heatwave criteria could be met in some parts of the UK.”