With the fan removed you can find the Part Number on the reverse side.

Googling this number gave me 2 options, a £45 replacement or a £10 one from Ebay.

As you can see, the fan casing is slightly special as it is open on one side and the edges of the casing are slightly curved.

What I didn't know is what my Ebay buy would look like, despite it being sold with identical Part Number the Suffix was different.