If the UK's Utility Providers have protocols similar to the Utility Providers here in USA
(more precisely, the "EUSERC-Related" Utilities of the Western / Pacific States),
there will be KVAR Correcting Capacitor Banks at the Distribution Yards, and at specific locations on the Distribution Feeder Circuits.
Primary Distribution Feeders are nominally 12,470Y/7200V 3PH. 4W, with some 24,000V and 34,500V Systems.
Older installs were 4160Y/2400 3PH. 4W, however these Systems are being Phased out where possible.
All Polyphase Transformer Primary connections are L-L Delta (12KV). Primary Side connections for Single Phase Pole-Mounted Transformers typically are connected L-L (12KV), but in LADWP Territory, the majority of 1 PH. Pole Mounts are L-N (2400V or 7200V).
In my area, the only L-N Single Phase Primary Terminations are for Pad-Mount Transformers.
KVAR Correction at Distribution Yards is placed on the 12KV Primary Distribution Feeders' side.
(BTW, in my area, the Sub-Transmission Circuit Voltage is 66KV, and the "Main" Transmission Circuit Voltage is 138KV)
The Yards have some PF Correction Banks constantly connected, and others connected per Time-Of-Use (TOU), via Cut-Outs.
For the remote locations (Pole Mounted Banks), there are some Permanently-Connected Banks, and some Banks which are connected via 15KV Oil-Immersed Cutout Switches.
A Time Clock, or Remote Controller opens and closes these Switches.
At each of these types of Correction Banks, there is a small (5 KVA maximum) 12KV to 120/240V Transformer, which supplies Power for the Control Equipment.
I am also interested in the UK's Primary Distribution PF Correction methods.
When you find the information, please reply!