If you have replaced everything and fitted them correctly then there can't be a fault. I suggest you take it to a garage that has worked on a fiat panda/fiat 500 and get a second opinion.

Noticed today with three in the car there was very little knocking!

Try the things suggested on page one and report back.
No worn bolts as long as they tighten up will not cause knocking.
The fact that when under more load (three people in the car) the knocking is less means you should be able to diagnose the problem as per video.

Go back and check the suspension bushes and ball joins.

Will do,probably next week though.

Sorry for taking so long to get back to you guys.I discovered the knocking noise was actualy the roll bar bushes which were only replaced in February!
There is about a centimetre play when the roll bar is pulled from the side.It's just passed it's MOT without it being noticed!

Well done

Just a quick update.
I fitted new anti roll bar bushes using better quality ones than last time,two bolts to take off each side and that's it,easy job.All quiet again.
Thanks for all input guys.