While we were living in London last year, a relative mentioned to me that a modern steam locomotive had been built in the UK and was running on the main lines sometimes. I looked it up, and found out about the amazing LNER Peppercorn Class A1 60163 Tornado, including the fact that it was scheduled to run a bank holiday service from London Paddington to Penzance while we were there. Given the opportunity to see a steam train leaving a main line London terminus, I dragged myself out of bed on a holiday Monday morning, and got down to Paddington to see it off.
I also used my phone to take some video, which I posted to Instagram at the time, and am embedding here too. Watching these with the sound is highly recommended.
I didn’t ride on this service and was limited to what I could see at London, but there are many videos from other people on YouTube, including this one of it racing through Twyford station: