Been helping my parents make some alterations to their bungalow they have
just bought, built in the 1970's and located near Scarborough, the walls
have that compressed straw stuff for insulation (internal walls too)
My dad was stumped to what these black mesh like panels were with single
electrical connections to them between all the rafters was,

He thought some sort of earth screen... maybe the last owners were paid up
members of the tin foil hat brigade and went one further to have a faraday
cage built above them

But as soon as i saw them i recognised them as electric heat mats, as i have
some reptile heating mats i use for injured birds i look after, black
tightly woven resistance mat with sewn on copper strips each side, placed
inside a polythene type bag, the edges of the poly bag are trapped between
the celing joists and the plasterboard celings, so it was put in as the
house was built it seems,

They no longer work, a lot of them have had the connector at the ends ripped
off taking part of the copper strip with them, and others have the cable cut
(a black outer, green inner and single stranded cable inside that,
terminating in a push on metal clip that is pushed onto the copper strip of
the mats, then tape put around the connector end)

No signs of any controller, but i imagine there may have been a frost stat
in the roof space to control them?

Am i right in thinking it was a way to keep the attic slightly warm to stop
pipes freezing and/or condensation forming? probably used in place of
traditional insulation?
The loft space is just the usual storage area, and i don't think over
ceiling heating is that good an idea... but there may well have been a
cowboy selling it in the 70's

I can only imagine the bungalow was built at the time nuclear powered
electricity too cheap to meter was on the cards,
Wonder what the police choppers doing thermal scans for drugs farms in
attics would make of the heat mats being on.