It's an early Mk1 'sinker' Xantia with faulty ignition switch, I sourced a replacement switch from KennyW that looked the same but when I'd compared it to the original it was different as can be seen here

The fitment to the lock barrel is totally different. I think the early type was only used for the first year or so of production.
I was thinking that replacing the whole switch and barrel assembly together might work and a Mk2 one is available. It would physically connect to the plugs but I wonder if anyone knows if the actual barrel itself will fit ok in the steering column tube.
That's the only thing that I think might prevent it?