I think that my blue, suede tassel loafers are on the "loafer" last, so I might be able to help.
I usually take a UK9 but, when buying loafers, I usually go down half-a-size. I did so in this case, too, and got a pair in a UK8.5.
They fit really well - fairly snug but not tight. There is a tiny bit of heel slippage, but not enough to give me blisters, and they are snug over my high instep, but are comfortable without any pain.
For comparison, I take a UK9 in the C&J 337 last and in Loake 1880 lasts such as the Capital and 026 lasts. I have quite a high instep, and my forefoot is fairly wide, but not so wide that I have to get wider-fitting shoes.