People walking along the Millennium Bridge, London, during a rain shower (Picture: PA)

The Met Office has warned that heavy thunderstorms on Friday could see half a month’s worth of rain lashing down in just six hours.

Buildings and structures could be damaged by flooding and lightning strikes while homes could also lose power ‘for a short time’, forecasters said.

There is also ‘a good chance’ drivers in affected areas could be delayed by spray and standing water, and rail passengers could face longer journeys.

Up to 40mm of rain is expected to fall in some spots across the south of England in just six hours. In a typical August, 63mm of rain falls there over the entire month.

Holidaymakers beginning their summer getaway are advised to check the Met Office app and social media channels for updates and brace themselves for longer journey times.

A yellow weather warning for thunderstorms has been issued by the Met Office for large parts of the South and the West Midlands between 6am and midday on Friday.

The area affected covers London as well as the whole of the South East and the Solent area, stretching to Birmingham at its northernmost edge.

A yellow warning for wind is in place across coastal areas of north and mid-Wales between midnight and 6pm on Friday – and gusts could reach up to 60mph.

Holidaymakers brave the rain on Blackpool promenade (Picture: Getty)

People walk in the rain along the sea wall next to the Palace Pier in Brighton (Picture: AFP via Getty)

People shelter from the rain in Brighton (Picture: Getty)

The Met Office said trees could fall down leading to train cancellations and likely delays.

Marquees and tents that may be used by campers in Snowdonia could also fall down in the gusts while caravans and lorries may struggle on some roads.

Homes could also lose power for a short time in affected areas, the forecaster warned.

Met Office meteorologist Rachel Ayers said showers will begin to fall in the south-west of England and south Wales before growing in intensity as they move eastwards.

A fan uses a denim jacket to shelter from the rain (Picture: Reuters)

People walking along the Millennium Bridge, London, during a rain shower, as the Met Office has issued a yellow weather warning for thunderstorms (Picture: PA)

Heavy showers could hit areas unaffected by the weather warnings but they are not likely to put people in any danger.

She said: ‘Given it is summer holidays, people are more likely to be wanting to be outside and travelling for holidays.

‘There is a chance we could see driving conditions affected, leading to longer journey times.

‘Take the advice from our partners such as the RAC with regards to driving in heavy rain if you do make that journey.’

She said conditions should brighten up across most of the UK on Saturday – with sunshine and showers likely amid ‘blustery’ conditions.

Heavy rain on Saturday is likely to be confined to the north-east of Scotland, she added.

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Buildings could be damaged by flooding and lightning strikes while homes could also lose power ‘for a short time’, forecasters said.