Royal Air Force (RAF) Air Chief Marshal Sir Michael Wigston said "it's 50/50" as to whether the flypast will go ahead as scheduled, with the final decision set to be made just one or two hours before it is due to start.

Forecasters predict Saturday will be a "cloudy, wet day" across large parts of the UK, with rain falling on London "by around lunchtime" - possibly hampering the ability of pilots to fly safely.

More than 60 planes from the Royal Navy, British Army and Royal Air Force, including the Red Arrows, are due to fly over the Mall and Buckingham Palace at around 2.15pm following the ceremony.

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The King and Queen are expected to watch the six-minute flypast on the palace balcony with other members of the Royal Family if it goes ahead.

However, the RAF has said low clouds and rain could mean it gets called off.

On Friday the capital got a taste of what is in store for the historic occasion after pedestrians and royal fans got caught in a heavy downpour in Westminster.

'Outbreaks of rain'

Met Office meteorologist Alex Deakin said there will be "outbreaks of rain in London from 8am onwards" on Saturday, adding it won't be anything "too heavy... it's just going to be a bit grey, damp and drizzly".

He added: "It won't rain all morning, just a bit on-and-off with some drizzle, it may stop for half an hour or so and come back again, that kind of thing.

"It will probably stay like that into the afternoon before it perhaps gets a little brighter but generally staying drab for most of the day."

Sir Michael said: "The weather isn't looking brilliant, but there's nothing we can do about it.

"We have to be safe, we have to make sure that we aren't taking any unnecessary risks.

"We'll make a weather call one or two hours before the actual moment, but if there's rain and low cloud then it will be almost impossible to get it through.

"It's 50/50 at the moment, but we have lots of options, the decision will be made, at this stage we're hoping for the best."

Highs of 17C

The King and Queen Consort's procession will set off from Buckingham Palace at around 10.20am, when light wind and rain is forecast.

Temperatures will reach highs of 17C by the afternoon, which is around average for the time of year.

The King and Queen Consort are expected to enter Buckingham Palace through the centre arch at 1.33pm following the ceremony at Westminster Abbey.

Mr Deakin added: "All the different aircraft have different criteria based on the cloud so it's obviously a call for the RAF to make, but it does look a little bit brighter come the afternoon compared to the morning.

"The cloud will be a little higher and there is a better chance of a drier spell, but the chances of sunny weather is almost zero and the chances of showers at that time is around 70%."

A Ministry of Defence (MoD) spokesperson said: "The latest weather information will be obtained from both the Met Office and from our helicopters performing weather checks in advance of the main flypast on Saturday.

"If suitable, the flypast will continue as planned. If not, then there are options available to reduce the numbers of aircraft, with cancellation being the last resort."

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A decision on whether the event can go ahead can be made by the RAF's Air Vice-Marshal Mark Flewin, Air Officer Commanding No 1 Group, or the aircraft pilots.

There will be a "north-south" split across the UK, with mostly grey and damp conditions in the Midlands, Wales and southern England, while northern England will be mostly dry until later in the day.

Meanwhile, Northern Ireland and Scotland are set to see a mixture of sunshine and heavy showers, with highs of 19C in parts of the Highlands.