Ian,
As said, for the scan you just lay still inside the MRI scanner. I think mine took 40 mins. It's completely painless, but they may want to use a Gadolinium contrast dye, in which case a machine will inject it towards the end of the scan (they'll tell you when it's going to happen, but it's painless). If you have the contrast dye, drink lots of water immediately afterwards so you pee it out as quickly as possible.
It's very unlikely the scan will be analysed while you're there. What usually happens nowadays is you'll get an invite to a one-stop-shop up to a week later. The invite is usually sent out before the scan is analysed, so it can't tell you anything.
You'll also get an invite for nuclear bone scan. For that, you get given an injection, told to go and relax and drink water and pee for a couple of hours, and then come back to be photographed with a gamma-ray camera, which I think took around a minute. One word of warning, try not to pee on your trousers, as it will make them light up bright white in the images!
At the one-stop-shop, they'll have the MRI scan result, and decide what to do next, such as a biopsy if appropriate. They try to do all the diagnostics on that visit, so expect to stay in the hospital for the rest of the day.
In know in a local NHS hospital, they've moved the one-stop-shop to a local COVID-free private hospital. COVID may disrupt some of the normal timings and orderings.