Electrickery, in fact it is mechanical.
When I pull the key out the steeringlock does not kick in, only after a tap on the barrel.
The barrel itself works fine but when I pull the key and open the door I get the 'key-in' message (beep) and a tap on the barrel lets the pin engage.
Before I take it all apart and do something stupid I like to know what the barrel does inside and what the best strategy is. Never done this before.
What I did dare is taking the shrouds off and replaced the blown barrel-bulb.
Tony.

The microswitch that deals with the Key In message is at the bottom of the keyslot and sticks due to a build up of dust and general crud. If you look you should be able to see a small strip of metal that the key pushes against. A good blast of brake cleaner should clean that out and not leave any residue for dust to stick to in the future. I've had my lock barrel out and it's an interesting exercise. There's a tiny spring that will fly out and you'll spend hours a) trying to work out where it came from, and b) trying to get it to stay in place while you assemble the lock again. You may well find that once you've cleaned out where the switch is, the steering lock will start to work again anyway as the brake cleaner will have gone further down and cleaned everything out. A bit of graphite powder in the lock itself will then keep everything moving nicely.

An easy fix, for a change, with this Tony.
Shrouds off, unplug connectors, key in pos 2, insert suitable probe in hole underneath to disengage holding latch, remove assembly.
Ignore RAVE which would have you remove tilt assembly and unscrewing stuff.
Once you have assembly out, remove key (don't attempt to get barrel itself out of assembly or bits will fly everywhere once key's out!), spray the hell out of it with suitable cleaner through the keyhole. I use electrical contact cleaner as there are plastic switches etc in there and I don't want to risk dissolving them with brake cleaner as I've seen others suggest.
Once the black gunge, running out of bottom has run clear, a blast through with compressed air, a shot of graphite.
Make sure that white gate at the top is moving freely (that's the key in/ out switch) and that it all turns nicely and key slides in and out smoothly.
Key back in. Push assembly back into column housing until it clicks. Check function again. Reconnect, shroud on, done!
EDIT- beaten to the draw by Gilbertd again. He has a different view of cleaner to mine, but each to their own. I could be wrong about the white gate at top being key in/ out switch as well, but that's what I decided when I studied mine!

Although I did suggest brake cleaner (purely because the contact cleaner I have seems to leave a slight residue). If you've got a contact cleaner that evaporates completely and doesn't leave a residue, then use that. I went a step further and took the lock apart, hence mention of the little spring and various other bits flying out.

Thanks guys, I'll see how I get along and post a pick of the lot if I get it right, as soon as I'm dressed and shaved ("don't you dare to go out there in pyjama's" Jo says).

Here are the pics
1: is this the pin to be pressed to release the barrel in pos. II?
2: do I remove this electrical part prior to pull the barrel out (disconnect battery?)

Do I have to remove something on this side of the locking mechanism?

1- I think so. It's obvious when you stick a drill (blunt end) in and can feel you're pushing a spring clip back
2- no need to remove that at all (or disconnect battery). As long as you pull the electrical connectors to the black bit in 2nd pic before turning key to 2 you'll be OK
The black plastic bit, barrel and light will all slide easily out from the column casting in the direction you pull the key out, once you've found the right pin to push

Done. A flush of contactcleaner, let it sit for a while again contactcleaner, a blast of comressed air and a puff of graphite did the job.
Thanks guys for your help.
Tony.

Don't you just love the simple ones. Not only that, but the satisfaction of knowing it's now all good every time you remove the key.