this is usually due to a failed ignition switch which is not expensive to have repaired, maybe £200 total.
the other possibilities for the cause would be a wiring / connection issue, or a failed control module of some kind. A failed module can get expensive depending on which (into the hundreds), and a wiring issue will only get expensive if it takes a long time to ferret out.
Again, I would say it is most likely the ignition switch which should be inexpensive and quick to repair.
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