Help - difficult to get in to gear

[JeffH]

Hi. After a 60 mile trip in the recent hot weather, I suddenly had a job to change gear. The stick would go in, but only with a hard push. The clutch pedal feels the same and before, and there are no fluid leaks under or in the car.
I have checked the clutch wear and have a measurement of about 26mm at rest with a travel of about 12mm measured through the hole in the bell housing.
There may be a small amount of play n the linkage at the gearbox end, but the gear change is not vague, just heavy. Any suggestions for me to check next?
Cheers all.