SID is an architecture type used in Telecoms by both BT and Virgin. It releates to the the Telephony architecture, you can tell as the pit lids will have a little badge with the Kite symbol (British Standard) and a stamp that says SID. Newer BT covers and Virgin SID areas will display this but only if the pit lids are elss than 10 years old.
There is also CAB architecture (also known as SBD) where the termination points arent normally in chambers in the ground outside your home but an entire cable run from the home back to a small cabinet (or pedestal) where the customer connection points are. This tends to be more commonly found in ex-NTL areas but is also found in small pockets of ex-Telewest areas as well.
BT uses SID architecture for its underground deployment, you will find an enclosure (referred to as a Bomb) with D side connections where customer conenctions first terminate (before heading to an E-side connection at the nearest cabinet (or distribution point).
http://www.hellermanntyton.co.uk/doc...logue_0809.pdf
See page 25 onwards of above document for more details.
Hope this helps