Steel frames tend not to fail suddenly - it likely won't snap. Perhaps ride it and jump up and down on the cranks in your garden/on soft floor to see if it gets any worse.
You can always get the tube replaced by a framebuilder.
@lae started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Steel frames tend not to fail suddenly - it likely won't snap. Perhaps ride it and jump up and down on the cranks in your garden/on soft floor to see if it gets any worse.
You can always get the tube replaced by a framebuilder.