Filbyman

You may have had a master or slave cylinder problem for some time. As the clutch plate wears it reduces in thickness. The new clutch will be thicker (and the new pressure plate harder to push) it will alter the position where the slave cylinder operates. If the master cylinder inside or seal are warn or damaged, it will not push so much fluid. If you put the clutch down and hold it down (while in gear) if the clutch slowly starts to engage then the master cylinder needs attention.
(silly question, you have bled the slave with bleed uppermost) Not worked on LHD cars, so if you can adjust master cylinder, try it (after the hold down test)