The back door light had some terminal thing in it, with two black neutral
wires, two earths and one red live. When I opened this up, there was an
orange wire loose, it could have come out when I opened it, not knowing
what it was I did not reconnect it. The red live and one black neutral go
to the electrician fitted light.
It may seem obvious that the orange wire is the main's live wire and that
is why the 3 lights don't work. However I am confused by the fact that it
is orange and am not sure if I should connect it.

If this is likely to be the problem I would appreciate some reassurance,
or any other information I could use to fix the problem.

From your description, it sounds like the orange wire has come loose (is the
terminal block where it looks like it was from loose, or does it contain a
small piece of wire that has broken off the orange wire?

The reason it is orange - maybe it is that particular manufacturers version
of red!

Can you take any pictures, or trace where this orange wire goes?

Sparks...