I found this an interesting read:
All the rules on how you can see Queen Elizabeth's coffin in Westminster
https://www.walesonline.co.uk/news/uk-news/rules-how-you-can-see-25022226Here's a few excerpts:
The queue starts where Albert Embankment meets Lambeth Bridge in Central London, on the south side of the River Thames. From Albert Embankment, the queue continues along the south bank of the Thames.
Those joining will be issued a wristband to mark their place and avert the risk of queue-jumpers. The wristbands also allow people to leave the queue “for a short period to use a toilet or get refreshments†before returning to their place in the queue. Public toilets, drinking water and first aid stations will be available at designated locations along the queue route.
Official guidance warns: “Please note that the queue is expected to be very long. You will need to stand for many hours, possibly overnight, with very little opportunity to sit down, as the queue will keep moving. Please consider this before you decide to attend or bring children with you. The queue may close early to ensure as many visitors as possible can enter the Palace before the Lying-in-State period comes to an end.â€
Separate access queue
People with a disability or long-term condition which means they are unable to queue for an extended period of time will be able to join a shorter queue. A separate accessible kiosk is to be set up at the Tate Britain on Millbank. Timed entry slots for Westminster Hall will be issued for people with access needs, who can then move immediately to join the accessible queue at Victoria Tower Gardens, next to Parliament. There will only be a limited amount of spots each day for this queue.
Security searches may also be carried out while people are in the queue – while stewards and police officers are expected to patrol, ejecting queue-jumpers and those deemed drunk.
It is not permitted to queue on behalf of other people or “reserve†a spot for someone else – the person queuing up will be the only one allowed entry.
