It's getting more frequent.....

But my immobiliser light keeps flashing and preventing me from starting my 99 Octavia TDi.

If I remove the Key and push it hard toward the ignition, it seems to always do the trick, one key seems to do it more than the other but they both work perfectly when you can get them to read...

Any fixes, I've briefly read about the immobiliser read coil...

Could I have some instructions of how to fix this for starting first time everytime!?

Thanks.

I'm getting worried about getting stuck somewhere in the dark etc...

I think as you've discovered, the coil is a good place to start.

But how do I replace said Coil?

I'd start off replacing the loom from the read coil to the back of the dash panel. This involves removing the steering column shrouds and the dash panel insert. The loom part number is 1U0971809 and should be well under £10.