Lack of fttc in central london
I have a number of clients across central london and we cannot get fttc anywhere - the exchanges are just not enabled - yet you see fttc enabled exchanges in Islington, Shoerditch etc, but not the City or Westminster.
To get decent service SMB's have to opt for Efm or fibre - though have had some luck with Relish recently offering 40 Mb over 4g