Hi,
Check that the cam followers drop away from the valves if you think you have stuck valves.
I have seen a few instances of split cam followers caused by overtightening the adjusters. the cam followers jam in the guides holding the valves open.
when you have a look at the followers, if split it will just look like a small vertical scratch. you need to pull the followers out and tighten the adjusters to see if a split opens up. or use a dye test kit.

you could try to loosen the tappet adjustment lock nut on the offending valves and see if it makes thing move.

Austin valves rarely jam in the guides unless they get bent.

Please report back on your findings.

Location: Cornwall

Thank you everyone for your advice. Sounds like the valves could coked up a bit. I have decided to take the head off etc and check nothing is bent or damaged and hopefully all it will require is a bit of a clean.
Will let you know when 'Ivy' is back running around my local lanes.