Image copyright Rex Features

Fog across the south east has disrupted flights at Heathrow, Gatwick and City airports, British Airways says.

The delays in London come as people travelling for Christmas were warned to expect disruption across the UK as Storm Barbara approaches.

The Met Office said the worst of the weather was expected on Friday and Saturday, with gusts of up to 90mph forecast in parts of Scotland.

It has issued an amber warning for northernmost Scotland to "be prepared".

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Though the fog has now cleared, a spokesman for Heathrow said some early morning flights had been been pushed back and there may be a few knock-on delays remaining.

British Airways urged passengers to check their flight status online, adding that some flights to and from London were being affected.

Image copyright PA Image caption Christmas travellers will be hoping to avoid delays, as fog hits flight arrivals at London airports

Gatwick was forced to divert five or six flights in the fog overnight, but has since resumed normal service.

London City, which diverted some flights to Heathrow amid delays and cancellations on Thursday morning, said the knock-on effect could cause further delays on Thursday afternoon.

The Met Office said Thursday would see a split day for the UK - wet and windy in the north with blustery showers, but mostly dry in the south.

Looking ahead, pockets of Northern Ireland, north Wales and the north of England are also set to feel Barbara's force.

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Grahame Madge, spokesman for the Met Office, said: "We have had the good fortune to be able to issue the weather warnings ahead of Storm Barbara coming, with plenty of time hopefully for people to change their plans if they need to.

"But the nature of the storm means it still has the potential to have an impact on power supplies, structures, and disrupt bridge and ferry crossings."

Expecting widespread disruption, the UK Coastguard issued a coastal safety warning, advising people to check the weather and tidal conditions before they set out.

Scottish and Southern Electricity Networks said it was moving engineers to areas it expected to be hit by the storm, while Northern Powergrid said it was bringing in extra engineers.

Storm Barbara has been named in line with the Met Office's alphabetical policy of naming storms when they are deemed to have the potential to cause a substantial impact in the UK or Republic of Ireland.

Barbara is only the second name designated this season, which began on October 1, and follows Storm Angus, which brought high winds and heavy rains to parts of Britain in November.

The storm comes as rail travel is being affected across the country because of strikes and 200 incidents of scheduled engineering works.

Although the next strike day is not planned until New Year's Eve, Southern Rail has warned of disruption every day because of an ongoing overtime ban from the ASLEF and RMT unions.

Elsewhere, major disruptions include:

All lines will be closed between London Paddington and Ealing Broadway between 24 and 29 December

As a result of this there will be no trains to or from London Paddington, including Heathrow Connect and Heathrow Express services

Arriva Trains Wales services between Manchester Piccadilly and Warrington Bank Quay will be replaced by buses

Manchester Oxford Road and Deansgate stations will be closed to trains on 27 December and from 31 December to 2 January

Northern trains between Manchester Airport, Blackpool North and Barrow-in-Furness are being diverted, running from Manchester Victoria instead

Although industrial action by baggage handlers has been cancelled, British Airways cabin crew are still planning to strike on Christmas Day and Boxing Day.

Talks aimed at averting the strikes resumed on Thursday, though BA said it would run a full service on both days.

Image caption Gusts of up to 90mph are forecast in parts of Scotland

Scottish Transport Minister Humza Yousaf told BBC Scotland the government was working with agencies to do everything possible to help people travel safely.

He said: "Ferries are particularly susceptible to disruption due to high winds and we may also see some disruption to flights.

"Those planning to fly or use ferries this festive period should check with their operators for the latest information and consider the forecast as part of their plans."

'Slow down'

Friday is expected to be the busiest day on the road for the Christmas rush, with traffic information company Inrix saying some journeys may take up to three times as long compared with other times of the year.

It predicts the worst affected routes will be:

M25 Reigate to junction 16 (M40)

A4 Earl's Court to M4 Reading

M5 Thornbury to Weston-s-Mare

M6 Stoke North to Warrington

M60 Carrington to M62 Rochdale

The RAC also warned that Friday would be particularly "tough going" for drivers, urging people to try to get away during the calmer weather windows of Thursday or Saturday afternoon instead.

Highways England warned drivers to be prepared.

A spokesman said: "Many people will be planning long journeys over the next few days to see friends and relatives during Christmas but it's vital they slow down during stormy weather.

"Rain makes it harder for tyres to grip the road and harder for drivers to see ahead - significantly increasing the chances of being involved in a crash."