Key won't go in ignition

Hi everyone,

I wonder if any could help me. I have a 306 D Turbo 1997 RHD. The other
day I tried to insert the key into the ignition as normal and for some
reason the key wouldn't go all the way in. Upon inspection, it looks
like the a pin which fits through the slot at the end of the key was
not allowing it to sit flush in the barrel. I assume this pin is to
stop the key being removed from the ignition whilst its turned. I can't
understand why this pin is engaged whilst the key is not in the lock.

Anyway to temporarily overcome this problem I cut a channel in the end
of the key with a hacksaw to allow the key to fully insert. This is
working at present but my spare without the notch cut can't be used.

Is this a common problem with a simple solution or is it a case of
either replacing the barrel or calling out a locksmith?

Anyway any help would be appreciated.

Thanks

Doug