I went to buy a new diesel fuel filter today for my 2010 Octavia. Was told that Skoda supplies two different diameter filters for this model. Can I tell from the outside or is it old one out and measure ?

If I remember right, there should be a sticker on the side of the filter housing telling you which filter type. You can just about see it with the bonnet open, down under the inner wing. Should say UFI something, or the other one! Mine is UFI (2011 Octavia), believe.

Okay cheers for that 

Found the label reads : UFI 3CO 127 400C

Filter to fit 3C0 127 434. Stick with good quality own spec brands. 

confirmed 78mm diameter filter. Bought Mann one. Do you have to pre prime the filter housing with diesel when fitting these ?

I would think that is a good idea.

Changed the filter today. Last filter date stamp : 6/10 which ties in with date of manufacture. No wonder it was covered in a rust type slime. At 100 k puts it 40k over its service date. The tick in the corresponding service box not true then ? Still live and learn.

Main dealer service history or independent? Done while you owned the car, or previous owner?

Might be worth getting in touch with whoever claims to have done the service...

Always had car serviced by approved garage then independent from nearly new. Should have paid more attention to service book. Modern  electronics / instruments could measure D.P across filter and relay to dash alarm ?