Britain is set to enjoy a summery spell as forecasters predicted the highest temperatures of the year so far.

The mercury is expected to hit 26C in some places over the weekend - about ten degrees above the average for this time of year.

The hottest places will be central and southern England, while sea mists will keep coastal areas cooler.

Most parts of the country will stay dry, although there is a risk of isolated thunderstorms in Scotland and northern England, but the country will cool off next week with temperatures likely to return to the May average of 15C.

Gemma Plumb, forecaster with MeteoGroup, said: "Temperatures will range between 24C and 26C from Friday to Sunday. The greatest chance of reaching 26C will be over the weekend. Sea mist will keep temperatures cooler in coastal areas, but further inland it will feel very warm. There is a risk of thunder storms across northern Scotland tomorrow and on Sunday in Scotland and northern parts of England."

Ms Plumb said warm, humid air was being brought to the UK this week by a high pressure system moving up from Spain, and added: "Cooler air will move in gradually next week, allowing temperatures to return to the average for this time of year. Although it will stay above the average for longer in the South."

Predicting the weather months ahead is notoriously unreliable. The Met Office predicted a "barbecue summer" for 2009, which was ultimately a washout.

The Met Office dropped long-term seasonal forecasts in favour of monthly predictions for Britain, updated weekly. But independent forecaster Positive Weather Solutions (PWS), which accurately predicted last year's wet summer, forecast great weather for the months ahead.

Jonathan Powell, senior weather forecaster with PWS, said: "The pattern through June is unlikely to be all that stable, so expect some rain as we pass through mid-month, although again, there will be some pleasant sunshine from time to time, keeping temperatures on the warm to possibly very warm side."

He went on: "July too starts on an unsettled note, with some rain around, but summer will emerge, and we can expect some decent drier spells and some warm to very warm temperatures. Towards mid-August, there will still be some pleasant weather around with long spells of sunshine."