Putting in my wiring for my sound system today, obviously need to remove the battery to get to the gromit to feed the power cable through and wondering if I will need a code for the stereo when refitting or is it stored on the unit when it's in the same car?

I have pulled mine out a few times and its never needed a code entering. I believe its coded to the key/car anyway.

No you won't. The code is stored in the car itself so is remembered after the battery is disconnected.

I have to recode the Symphony Radio/CD unit on the old Fabia when I have to remove the battery, to check steering oil level.

The four digit code was in my Symphony Radio/CD handbook when I bought the car new, so was a simple task.

Failing that, call at a Skoda Dept. and ask for the code, would be my first suggestion.

Rider to my previous comment: any CANBUS controlled car will store the code.