Cagey, if you take the Volvo part numbers into any good motor factors they will be able to look up the equivalent numbers for sensibly-priced filters that they will have in stock.
Original PNs:
Oil filter 834337-8
Fuel Filter 840532-6
Nowhere near my boat, so I can't tell you the number, but Halfords do an oil filter. It was the only one the same size and shape.
I didn't see one for the fuel filter, but at a tenner a go, I'm VERY interested in finding a sensibly priced one. A quick Google came up with a Fram equivalent - P4102, but no on-line suppliers or prices.
Be very careful with fuel filters - some third party filters are cheaper because they contain less filter packing. If one assumes that the filter packing is the same grade as that used by the original supplier then the third party one will block more quickly (less surface area), if it is a poorer grade to avoid rapid blockage then bigger bits will get through - the filter is there to protect the pump and injectors from crud - at one or two filters per season even the original fuel filters are cheap in comparison to a set of injectors (£100?) or a pump rebuild (£400?). I learnt my lesson when using cheaper alternatives to a Delphi / Lucas 296 filter to save a couple of £, now I will not fit anything else (but buy from a Delphi motor dealer).