The Mondeo Mk 4 uses a PSA manufactured diesel engine (DW10 and DW12). These diesels use a DPF (diesel particulate filter) to reduce particulate emissions. If you don't care about the environment then use the ACEA A5 oil which matches the Ford WSS-M2C913-A (and B and C and D) spec. If you do you should be using C1 or C2 which have much lower SAPS (Sulphated Ash, Phosphorous and Sulphur) than the A5 spec. I don't know why Ford specifies WSS-M2C913-A for the diesel as it is not a low SAPS formulation. I spent hours discussing this with various Ford personnel at the dealership and they were frankly clueless. Peugeot specify a C1 or C2 formulation for the same diesel engine when used in their cars. I use a C1 as I cannot find a C2 where I live. C3 is also an option but has higher viscosity so fuel consumption may increase slightly. Fiat, Mercedes and VW often specify C3 for their diesels with DPF.
There is a newer Ford spec WSS-M2C 950-A (which applies from 2014 onwards, ie. Mk 5 Mondeo) which is a C1 formulation with better cold start performance (0W30 vs 5W30 for the Mk 4).
The following are useful resources:
https://www.acea.be/...-sequences-2012 this is probably not the appropriate document as the DW10 was first produced well before 2012, but it shows the differences between the A and C series oils. I could not find the older ACEA documents with a cursory search.
https://www.opieoils...c-694-ford.aspx - lots of different Ford oil specs, the closest to the Peugeot spec is Ford WSS-M2C 934-B