I'd check with TrunkNetworks (Drew, their director, posts here frequently particularly in the Business ISP section).
I'm not sure who else to try. In general though, you'll need to arrange a trench or some sort of access back to the point of presence - typically this would be the exchange, although could well not be. Expect to pay a shed-tonne in upfront fees to get that fibre run completed, followed by plenty per month for the uncontented bandwidth.
Was on Xilo C&W LLU on MRCEN, Now Be* on MRARD.