An update to my initial post. Local dealer had our car for 6 days, diagnosed a failed gearbox mount. Apparently it is filled with fluid, not ours, it had leaked. Took two days to get the part goes someway to explaining why they had the car Mon through Sat.
It has fixed two of the problems. The 'clonk' has gone, as has the clutch judder. Makes sense if the gearbox/engine was moving on a failed mount
The gear change isn't fixed and I'll be pursuing this further. It is still very stiff going into first, more than half the time. Playing with it at the weekend. Engine/transmission warmed. Stop at lights, into neutral, clutch up. Depress clutch, into first and STIFF. Keep foot on clutch and it goes in and out of first oh so easy after the first time.
Now do the same, but after going into first, bring clutch back up and down again. Each time I do this it is a big push to get the car in gear
I'm guessing it is a synchro problem or clutch issue as I think the synchro is being forced each time, first time. Once it is in gear, in and out of neutral with the clutch depressed is how I think the car should be
I've bought a cheap set of Argos scales so I can try and measure the force to put the car in gear
To other Jazz owners: is the effort to put you car in first gear the same as moving it in and out of gear with he clutch in?
Thanks all for our comments