It might be the world's oldest model railway locomotive, but if you want your trains to go somewhere you need to head to York to see the L&Y Railway's working layout built in 1912 for their signalling school. It was still in use by BR up until 1995 after which it passed to the Science Museum and has been restored to its 1925 condition and is now on show at the Railway Museum.

https://collection.sciencemuseumgroup.org.uk/objects/co213140/model-railway-layout-lancashire-yorkshire-railway-signalling-school-model

It's now demonstrated using modern RC powered locomotives as the originals are rather fragile and the associated electrics are old enough to make the Health and Safety inspector get a bit twitchy.

Steven B

I remember this layout very well as I visited it twice as a child on Sunday School Visits. Then, shortly after starting my BR career in 1961 in Hunts Bank I attended the school for two years for evening classes whilst taking the Block Signalling classes. Unfortunately the railway itself was not used on these occasions as it had been on the Sunday School visits. I remember all the rolling stock was L&Y vintage. In the 1980's, when I was working at Crewe and in charge of the LMR Safe Working of Trains course the Inspector in charge of the school was on my team of Instructors and I was invited to the school on a few occasions to discuss course issues with him. By then the Inspector had added overhead wiring and an Electric Multiple unit to teach electrification issues (it already had third rail). He had also acquired a motorman's controller from a Bury line EMU which he was using to control the trains on the layout. On my last visit he told me of the plans to send the layout to York museum. Some years later I attended a series of meetings in a conference room in the museum and saw the layoput in a side room but not on public display. After the layout was removed the signalling school was split into two rooms. In one was a lever frame with block bells for traditional signalling and in the other was a push button signalling control panel. Both layouts had the same track layout so you could see how the railway had progressed. Happy Days.

Ron

Not the oldest, but rather large.  Well worth a visit.
https://en.wikipedia.org/wiki/Pendon_Museum