A. GHOST. Don't EVER use fuel additives
B. shaun. There is no such thing as leaded fuel available in the UK and hasn't been for years. If you are referring to the red fuel pump at petrol stations then it is LRP or lead replacement petrol and is NOT the same as leaded.
Either way unleaded fuel is absolutely fine in all A98 and A114 Qualcast engines providing you change the spark plug to an NGK BP-4. This is in accordance to the Atco/Qualcast issued service bulletin.
pleasant, July 2010