Hi Renluop,
There are two sizes of FTTC.
The larger one usually contains four 100 Pr link cables to the PCP giving a total capacity of 200 services (twisted pairs) using the SMPF (Shared Metallic Path Facility). I.e. it still has the telephone line back to the exchange connected as indeed is mandatory as BT's Ts & Cs stipulate you must hire a telephone line from BT wholesale or retail in order to receive the faster FTTC service. Smaller ISPs such as Rutland have a greater FTTC capacity which can be up to 500 if the MSANs are so populated as they use the FMPF (Full MPF) or isolated D side twisted pair.
The smaller one has only two 100 pr cables so it can only support 100 services. BT seem (at least in this area of Surrey) to use the small cabinets when the PCP has up to about 400 pairs.
On the THGI Guildford exchange there are about 38,500 lines but only about 12,600 FTTC pairs capacity spread over the entire area.
This is probably a commercial decision based upon the fact that the superior coaxial Virgin Media 100 Mbps service is available over a large part of the area; sadly there are quite a number of pockets without VM coverage. A few of these don't have the BT FTTC service either so they are just as badly off as many rural areas around here.
N.B. the above data are based upon my local observations without any formal confirmation from either VM or BT.
Kind regards,
Walter