Any bill that hasn’t received Royal Assent by the end of a session falls. But a Government bill can be preserved. A minister can table a motion known as a “carry-over motion”. In the next session, a carried-over bill restarts at whatever stage it had reached in the preceding session.
Carry-over motions only apply to Government bills and don’t apply to bills that started in the House of Lords. A bill can only be carried over once.
A carry-over motion extends the life of a bill to 12 months from its first reading in the House of Commons. If the bill won’t reach Royal Assent by then, the Government can ask the House to agree to extend the deadline.
Bills (with the exception of Private and Hybrid Bills) cannot be carried over between parliaments (i.e. following a general election).