On 11 Sep, 09:54, Boltar wrote:
For the first time today I waited on the southbound line to moorgate
at highbury. I noticed above the track there was what looked like
catenary strung up above the track all the way along and then it
disappeared into the tunnels. It also looked pretty old and given the
lack of any serious insulators theres no way it could be 25Kv. So was
it some abortive attempt at 750v DC overhead or was it something else
entirely?

It is an unpowered overrun wire, to guard against a train running with
a raised pantograph. It was installed at the time of the BR takeover
of the line.