As above!

My sister has just bought a basic skoda fabia as her first car! However, the dashboard lights, especially the speedo illumination is VERY dim! We have tried adjusting it on the scrolly adjuster bit and it doesnt get any brighter! We have even sourced another unit from a breakers yard and tried it and still no luck!

Anyone have any ideas on what could be causing this problem?

If the scroll dial unit has been replaced and it's still not bright enough, you need to have it code scanned. It might be the actual instrument cluster that's faulty. IIRC the 5V regulator for the dash LEDs is part of the instrument unit. It could also be a problem with the voltage control unit (behind drivers side parcel shelf. You may also want to check the fuses, and make sure none are blown, or have contact corrosion.