The warning covers London, the South East and South West of England (Picture: AFP)

Heavy rain and thunder is expected to thrash the UK on Saturday, putting a damper on Platinum Jubilee celebrations.

A yellow weather warning is threatening to turn picnics into soggy sandwiches, with the worst-hit areas facing frequent lightning and downpours.

The alert covers London, the South East and South West of England.

The Met Office said there is the possibility of thunderstorms moving north into southern counties of England during the early hours of Saturday, when frequent lightening and rain is expected.

Although the downpours will ease later in the morning in some places, others could see 20-30 mm of rain within an hour, with a small chance of 50 mm in two to three hours, most likely near the south coast.

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As a result, there is a small chance some homes and businesses could be flooded.

There could also be damage to buildings from floodwater, lightning strikes, hail or strong winds, The Met Office said.

This could cause some transport disruption on a day when thousands of people will be out celebrating the Queen’s historic 70-year reign.

Over 60,000 people have have registered to host Big Jubilee Lunches on Saturday, with events ranging from world record attempts for the longest street party to back garden BBQs.

A concert is also being held on Saturday evening at Buckingham Palace, with a star-studded line up including rock band Queen, Diana Ross, Alicia Keys and the UK’s Eurovision competitor Sam Ryder.

Twenty-two thousand people will attend the event, including 10,000 members of the public who won tickets in the public ballot and 7,500 tickets which were designated for key workers, members of the armed forces, volunteers, and charities.

The weather for the historic four week bank holiday has been good so far, with the sun shining yesterday as thousands descended onto the Mall for the Trooping the Colour.

There are no warnings in place today, but scattered thundery showers in central and western areas are forecast.

Sunday is also expected to be a washout, with heavy rain in the north and south.

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Queen Elizabeth II’s Platinum Jubilee 2022