I'm new to this forum, after having a quick browse, I've come across similar issues to this mentioned, however, no-one with the exact issue (to the best of my knowledge!)
As you're all a bunch of experienced chaps and chapesses, I thought I'd bring the problem your way, see what you make of it.
I'm currently getting some issues with the immobiliser on my 147, basically only about 25% of times will my key actually start the car. The other 75% of times, it looks like the immobiliser is saying no! When the car does indeed start, it will cut out (to my horror) wherever it sees fit to which I'm greeted with a 'Immobiliser Failure' message and a key symbol.
I first of all thought this was a battery in the key issue, however, upon reading it seems that this component in the key actually requires no power!, so I guess that puts that idea out (unless the component in the key is faulty)
Basically, I was wondering if this is a known issue because at the moment, I am without a car or at least one that will stay going if it does at all!