I had the same
problem with my 56 plate 2.0TDI 140 Ref Sport a few months ago.
I was getting 3 fault codes via the diagnostics, the important one was P3103 but there are some more with the last digit changing that are potentially the same
problem.
After much reading, I found the part number to be 038128063 L/M (7.14393.26.0). The letter at the end changes inline with updates being made to the part by the manufacturer.
I bought the part from Murrays Direct (01707 272686) they have a .co.uk web site also. Including next business day delivery it was just shy of £200.
I got a mechanic at a local garage I use regularly to replace it, it took less than an hour and needed a fuse also.
From memory the fuse is F23, F8 is for MY up to 2005, F23 is for MY 2006 and beyond.
Hope this helps.