It's looking like I will get my kitchen units from DIY-kitchens. I've mapped out the design and like what they have available and their price is competitive. The only problem is that the main worktop run is a bit over 4m and the island is worthy of its name and too big for their standard sizes.
I got a quote from Worktop express by emailing their fabrication department. They got back to me with the quote in a couple of days and it's very competitive. I was originally seduced by some flashy looking granite but kept getting drawn back to solid walnut and that's what I've got the quote for. I received my samples yesterday, too, and they are very lovely and go well with the door sample that I ordered from DIY-kitchens.
Worktop express are certainly worth checking out.