You can't buy UK10,5-UK11 shoes with those measurements, you will have like 5 cm in front of your toes and the flex point will be all wrong. Sucks to have "weird" feet, but if you end up buying ill fitting shoes even if they are cheap they will end up very costly. I mean you are probably more of a UK7,5 very wide fit or something like that. The best option might be to go MTO with a company that offers extra wide fit. Not sure if Meermin does, they do offer wide fit, but for example Vass offers their shoes in H-width (standard is F), and their MTO costs €520 which is very good considering they are completely hand made with oak bark tanned soles and great materials.
Couldn't agree more - buy a last that fits. I see a lot of pics on this forum of guys who have a shoe that's at least a size too big on a narrow last: even if it's not uncomfortable, which it often will be, it ends up with the toe of the shoe looking like a separate being, pointing off askance with a life of its own. Check the G&G thread for obvious examples! Or pretty much anything French.
I'd be interested to know what shoe you have now that fit well.
For reference Man of Paisly, my feet also measure some 260-265 mm and I have so called 'low footvolume'. (In contrast to you?). Albeit I have 100-105 mm wide feet. I am looking at sizes that range from 6 UK F (Loake capital) to 7 UK (dependent on fit). I can't stand roomy toeboxes or huge flexing near the ball of feet area. Like J Ingevaldsson I suggest you size down and go MTO for a wider width. Alternatively you could check out brands like Cheaney on Ebay. Alot of sellers regularly add shoes of F or G-width there.