Does anyone have any experience with replacing the ignition barrel on series 3's
Its a 2 1/4 petrol, non locking, the key was pretty lose when I got it, it rattles about a bit and can be removed with the engine running, its playing up a bit more now so time for a new one, Lucas do one for about £17, is there a better one on the market.

I had to replace the one on my 1977 lwb station wagon, it is the one with the steering lock. The whole thing had to be replaced and I got a new, 'old stock' barrel for about £50. It was a bit fiddly but not difficult, it was harder for me because I have gorilla like hands. Steering wheel doesn't need to come off but it makes it a bit easier to take it off, then plastic shroud. Two bolts hold it to the column then its just a case of being careful about removing the wiring connections, take pictures of the old one before you disconnect so that you can put them back in the right place. Lucas locks in the 70's were never that great but one should last a good ten years or more. My daughter had to have the ignition barrel on her Jazz changed recently, her key ring has about a kilo of crap hanging from it and this helps cause damage, don't have anything unnecessary on your ignition key ring.

Col

The non-steering lock switch is quite easy to replace. In theory you can replace just the barrel, but the whole switch isn't much more expensive.
I replaced the switch on my LWB a year ago with a cheap blue box one while I got the steering lock sorted and it's been ok (and the steering lock one is still on the bench waiting to be fitted). I prefer to use genuine Lucas parts if they're not silly money, but at £5 for the blue box one, it's not a big deal if it doesn't last more than a year or two.

Yes, aim to change just the lock barrel not the whole unit. The "tumblers" are just very thin brass strips that wear. Do it while the key still works as once it doesn't its 10x the job.