Lets start with a few basics. There are about 25 Million homes in the UK with about 50% passed by VM so about 12 Million so currently about 12.5 Million homes not served by VM so VM are looking to expand their coverage by about one third and the only way they can achieve that is by going into the larger rural towns, These are not small town you are probably looking at towns in the region of 50,000 people
Let's continue with some demographics, so we can understand the picture.
I have good figures for England+Wales - harder to find the equivalent for Scotland & NI. With this in mind, I'm assuming that E+W gets their fair share of the additional premises - so around 3.5m of the 4m premises.
In England & Wales, there are 5,500 places (from hamlets to cities) that the ONS classifies as "built up", and 95% of the population live in these places.
However, 50% of the population (and 49% of the households) can be found in just the top 31 of these places, with the smallest (Blackpool) having a population of 240,000 people.
To add 3.5m premises of additional coverage, you would now need to cover the top 100 built-up areas, with the smallest (Maidenhead) now having a population of 65,000.
The kind of place that will be at the tail end of this extra coverage include: Maidenhead, Wrexham, Folkestone, Newbury, Tunbridge Wells, Stafford, Lowestoft. The ones just outside the boundary would include Taunton, Macclesfield, Kettering, Runcorn.
I'm not hugely convinced that we tend to think of these places as "rural towns", but just "towns".
Note: To include towns of size 50,000, you would need to add another 28 places, and extend coverage by an extra 750,000. The tail would now have towns like Llanelli, Wellingborough and Horsham. Outside would be Bromsgrove, Banbury and Durham.