Book about Victoruian steam lcomotive being hidden under bridge arches?

[cantkeepawayforever]

I know you lot are brilliant, so here goes...

A children's book, pre-mid 1980s (could be older), which featured a prized steam locomotive being ?hidden under the arches of a railway bridge, probably in London, and then rediscovered?

I can't remember if there was a ghost or old man element to do with the inventor?

Does it ring any bells for anyone?

The only one I can think of is Thomas the tank engine where Henry gets bricked into a tunnel because he doesnt want to run in the rain. Could that be it?

No, definitely not that one. It's about a gang of boys - or a single boy - who finds this historic train.

The Viaduct by Roy Brown?

YES!!! I really do think that might be it! I'll get hold of a copy to check, but that's brilliant. i've been looking for this book for years!