I use 5w 30 oil, suitable for VW 504 & VW 507 engines. RAC branded fully synthetic purchased from a local supermarket for topping up.
Fortunately same oil as my wife's Skoda Fabia 1.6 TDI.If you give your local dealer a ring they'll tell you.
These are Halfords own branded 5W 30 oils but note they are manufacturer specific. And note how some are fully synthetic whilst others are part synthetic. If you have a look at the major brands, your Castrol Edge's etc just make sure the VW502/504 etc specification is listed. You need to be careful which oil you chose especially when running in long-life mode.