You need a rear facing seat for a baby that age. Are you on FB? It might be worth braving the wilds of the FB car seat groups (make sure you pick a UK based one as American car seats are different) because they tend to have more experience with ERF and can tell you what will fit in a van. Or you could look for a local ERF specialist and ask their advice about which seats they have fitted into vans as well. If you go onto the website for Axkid, those are the most popular imported brand and they have a stockist search and anyone who sells Axkid will usually have knowledge about ERF. These seats are all belt fitted.
Legally, it's a bit messy at the moment because you can still buy car seats according to the older regulation (R44) which go by weight "groups", so he could under that regulation go into a forward facing seat as he's over 9kg. However, would really strongly NOT recommend this, obviously it's better than nothing, but at 10mo, he'll be at very high risk if you were to crash with him in a forward facing seat.
Otherwise if you bought a seat which conforms to the newer regulation R129, which are usually height based, legally he needs to be 15 months AND at least 76cm to go into a forward facing seat. And 15 months is really a bare minimum. It's better to keep him rear facing as long as humanly possible.
Ages are usually given as a guideline - it's only that 15 month age minimum for forward facing, which applies to R129 seats (which are the majority of car seats on the market these days).
Does he still fit into a baby rear facing seat? I would keep that for as long as possible, they can use those until their head is at the top or the weight limit is usually 13kg, whichever comes first. And then potentially seek out either a rear facing specialist near you so you can try multiple seats and see what will fit, or try some of the cheaper seats like Joie Tilt, Joie Stages, Graco Extend, Halfords Impala, Graco Slimfit/Joie Every Stage R129 and see which ones you can see past to the mirror, which is obviously a legal and safety requirement.
If your van has passenger airbags, you will need to disable them to use a rear facing seat in that position.
I will second the Joie Stages as being an option as I know someone who used it rear facing in the front of their Transit.
Once baby is 15m+ if you do end up opting for a forward facing seat, I would probably recommend Britax King Pro as being the best forward facing belt fitted option safety wise. But look into rear facing if you can!