People hoping to pay their last respects to the Queen may have to queue for 12 hours to see her coffin, royal experts fear.
Officials expect that the queues to see her coffin could stretch back for miles when she is left to rest in state.
Rail firms have warned that trains will be ‘extremely busy’ as people jostle to see Elizabeth II one last time.
Westminster Hall will be open for 24 hours a day for four days to allow the public crowds to view the Queen’s coffin.
‘Insiders’ told The Sun that the queue could stretch three-miles, perhaps adding to the remarkably British feel to her send off.
It follows the death of the 96-year-old on Thursday afternoon, which has made her son King Charles III the new monarch.
Whitehall chiefs looking after the logistics behind the historic vigil believe mourner numbers could be around that which turned up to view Pope John Paul II, the paper reported.
Around one million mourners filed past the late pope as his body in 2005, when his body lay in state in Rome.
The Rail Delivery Group has meanwhile warned those wanting to travel to Westminster Hall to expect services to London and all of its stations to be packed.
The rail operator’s customer information director told the BBC that people should plan carefully and allow plenty of time if planning to travel during the official mourning period.
That stretches until the day of her state funeral, a week today, on Monday September 19.
Transport for London also warned that roads and public transport in the centre of the capital will be very busy.
It advised travellers to allow ‘plenty of extra time’ for journeys and to avoid driving where possible.
Andy Byford, London’s Transport Commissioner, told the BBC: ‘We are working with our partners to keep our city moving smoothly and to ensure that everyone who is planning to attend the memorial events can do so safely.’
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