No there isn’t. The old railway lines run North and South of the Square. There may possibly be an unknown Williamson tunnel down there somewhere ( the buggers are everywhere) but there isn’t one we know about.
Where did it come from?
When the sewers were dug out through the rock from MossLake fields to drain the ground for construction, the major Oxford Street channel was known as ‘The Great Tunnel’. Most of it was infilled afterwards with only the sewers remaining.