There's only so much granularity possible in a scheme like BDUK. Long lines (>1.5 km from the cabinet) are a particular challenge that may well fall through the gaps, as they are often highly geographically dispersed and low in density.
In some cases, network rearrangement may allow the creation of a secondary connection point closer to the served premises, and it would be possible to site an FTTC cabinet there. I'm not sure whether BT Openreach do this in practice - it's merely a possibility.
In many cases, the long lines are so geographically dispersed that there's no way to rearrange the network to create a viable deployment scenario for FTTC. The problem is finding a site for the cabinet that gives worthwhile predicted speeds for the end users without complete network reorganisation and running new lines from subscribers to a new cabinet (which is extremely costly - if you're going to go to all this civil engineering trouble, you may as well deploy FTTP whilst you're at it).
The obvious answer from a technological standpoint is FTTP, but the installation costs are far too expensive for the limited funds available, particularly from an 'investment per served premises' standpoint. The distances involved only serve to increase the cost per premises served.
If there's 80 long lines on a cabinet, in four rough groups which are all of relatively low density, the only economically viable solution for superfast broadband for those premises is likely to be wireless - fixed wireless (4G / WiMAX, Wi-Fi using specialist antennas) if the population density and terrain are favourable, satellite if not.
A good analogy is mobile phone network coverage targets. Getting to a certain proportion of population is fairly straightforward for the mobile networks - start in the major cities and build outwards in descending order of population density. At any given time, the low density of potential users and the challenges of terrain form an upper bound on the level of coverage economically deployable. Large and sparsely-populated areas are typically the last to be covered.
With both mobile phones and BDUK, it's important to remember the difference between proportion of population served and proportion of land mass covered. BDUK is about fixed users, so does not have the problem mobile users find of coverage disappearing when they move away from populatid areas. There will be areas, especially in large and sometimes sparsely populated areas like Suffolk and Norfork, where there is quite reasonably no need for superfast broadband.
BDUK, at least in the incarnation we have now, never promised 100% superfast coverage.
BDUK's aim is to get a superfast fibre-based service or an equivalent to 88% of population by end 2015 and 95% of population by end 2017. This will inevitably mean selecting the properties that are easiest to serve and deploying networks there, leaving the rest unserved. The maximum public benefit is derived by serving the greatest number of properties with the available funds. It is not possible to providing 'at any cost' solutions for the most difficult to serve areas, and those areas should not expect to receive anything from BDUK.
There's also a 2Mbit/s universal service obligation - but that's not really what we're talking about here.