[IainG]

Hi
What engine??
With the 2.0 D :- Generally with the ignition switch the engine won’t turn over and sometimes get “key error” message.

There are issues with sticking flaps in the throttle body. If one sticks shut it can fail to start.
Also there have been issues of cracked fuel filter housings and/or leaking o rings on the fuel line connectors.
I assume your engine turns over but doesn’t start??
Probably not the ignition switch.
Try the air flaps first and then for air leaks in the fuel system. There is no lift pump on these engines so any air leaks in the fuel system and fuel can drain back to the tank and cause starting issues.
Loads on the forum about the air flaps, just do a search.