Clutch pedal will not press down at all

Any ideas /usual fault for this? Thanks.

Did you check the basic thing first - is there something stuck behind the clutch pedal?
Second option could be a faulty clutch master cylinder.

It has been left standing a while!

More than likely a seized clutch arm, they have a tendency to seize up where the shaft goes through the housing especially if they have been standing a while. Can be freed up but they are a bit awkward to do, Mine was getting a bit stiff, but I had it sorted when the clutch was replaced a couple of years ago. It was removed, cleaned and re greased.
Try some penetrating oil and see if you can work it loose, you may need someone to operate the clutch while you try to lubricate the arm.
You can access it from the top if you remove the engine access panel. Don't use WD40 as its not a true penetrating oil. Plus gas or Rocal or similar make is best.

Sundance

Do not keep pressing the pedal in the hope that it will clear, the chances are that you will blow the slave cylinder.

Agree with all of the above.

Disconnect the slave cylinder pin, then trickle plusgas into the housing around the shaft and use a length of tube slid over the arm to get a little more leverage to gently wiggle the arm free.

Ideally the bell housing would come off and the shaft come out to remove any pitting and to regrease it, but this is non-trivial in the F/TF and you may get away with working it loose and then trickling a medium density oil in.

A better long term solution is to replace the clutch arm with one like the Mike Satur ones with a grease nipple built in.