Tri-ang (part of Lines Bros.) made TT gauge models from 1957 to at least 1967. It was built to a scale of 3mm compared to that of 4mm for their OO range.
The name "TT" came from the phrase used to describe this smaller scale: "Table Top".
What's it worth? Take a look at this Tri Ang Tt price guide: sold listings for a value indication.