The warmer it is, the faster it will deteriorate. Further, the faster
the film, the more quickly it will deteriorate. I wouldn't worry too
much about occasional high temperatures, unless the film has been left
in the boot of an automobile while it sat in the sun.  That's a real
no-no.

You will typically see a color shift with older film, and perhaps a
shift in the effective speed as the film ages.  If you take some sample
exposures, and they seem to be OK, then your film is usable.  If the
color has shifted, then it is not.  You can correct some color shifting
in your scanner, such as from old slides or negatives.

Since it's positive film, you will be able to see if it is properly
exposed, and if it has the correct color balance before you get to the
scanner. That eliminates one item from your list.  If your camera and
meter work with other types of film, that eliminates another two. That
leaves the film and you as the suspects, if the photos don't look
right.  Not an easy choice, I'm sure.

Not necessarily.  The whole idea of professional film is that it is
consistent.  You can take a photo on another roll of film from the same
batch with the same lighting and composition, and get a result that is
virtually identical. This is important where a photographer might have
to take another photo to correct some composition problem, and wants
things to fit into a series of photographs.  

Such consistency might not be the case with consumer film, where
exposures or colors might be slightly different, such that the
replacement photo would stand out in an otherwise sequential series of
photos.

In your case, the film will have shifted, and will not be the same as a
roll of new film.  As with consumer film, it might still be acceptable
for your uses, as long as it hasn't shifted into colors that are
obviously wrong.

Not me.

Sorry, I'm not in the U.K.  Every film will be different. Sometimes with out
of date film you see less Dmax. Sometimes a color cast or shift. You have to
try and see what it does.

Throw it away.