Friday is already above average for October, with 22C or 23C forecast in parts of the South and Midlands.

The Met Office says "increasingly warm air" on Saturday will increase UK highs to 24 or 25C (75-77F), before Sunday brings even warmer conditions.

"Temperatures are likely to peak on Sunday in the mid - possibly high-20s - and could get to around 26 or possibly 27 Celsius," said Met forecaster Alex Burkill.

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Those Sunday highs are possible in southeastern England, with the low to mid-20s widely expected elsewhere, and mid to high teens in Scotland and Northern Ireland.

However, there is a clear north-south contrast over the next few days, as much of Scotland and parts of Lancashire are forecast to get heavy rain.

Weather warnings have been issued, indicating the potential for life-endangering flooding and disruption, in some areas of western and central Scotland.

A yellow warning begins at 1pm on Friday in Lancashire, covering areas such as Preston, Blackburn and Burnley, until 3am.

Scotland has a yellow - and a more serious amber alert - covering much of the country from the early hours of Saturday until 6am on Sunday.

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There could be more than 150-180mm (5.9-7.1 inches) of rainfall over higher ground and 80-100mm (3.1-3.9 inches) at lower levels, according to the Met Office.

The warm temperatures are expected to linger into early next week - with high-teens to mid-20s and sunny skies on Monday and Tuesday, before things turn cloudier and cooler.

Sky News meteorologist Chris England said this weekend's highs are about 10C above the October average, but still well below the record for the month: 29.9C (85.8F) in Gravesend on 1October 2011.