afaik a "plug top" is the correct term for what is commonly known as "a
plug" (usually a (2/5/13A fused plug). 4 gang extension lead is simply
an extension lead with 4 x (13A) socket outlets on the end! (y/n)?

I think you must be making this up! Neither wikipedia nor any of the
online dictionaries know the term. "Plug top"...so what happened to
the rest of the plug?

I have never heard anyone use the term "spare way", though I have to
admit it's quite common to say "4 way extenstion lead". "Spare socket"
is what "normal" people say... :-)))

They are technical terms that would be understood by any electrician or
person competent in electrical works. As this is a technical newsgroups,
their use is perfectly acceptable.

Christian.