Having now stripped the tracks, suspension arms and wheels (suspension wheels between the idler wheel and the drive sprocket wheels) I believe the fault is the suspension.

One of my suspension tension springs was not located correctly causing it to bind and thus not move freely and some of the others where not a free moving as they should be.

The long arm of the suspension tension arm spring must have a slight outward bend to make sure that the spring arm is always located in the suspension arm. To much outward angle is just as bad as to little as too much causes the spring to bind.

If I can obtain just the springs and the cost of postage is not silly for such light items I will buy and fit new springs.

All the above assumes that the tracks are not to long.
Since an unmodified tank has plastic bearing surfaces to much track tension will wreck the plastic bearings and introduce even more slop.

My understanding is that the key to how the track system works is the suspension system.

If the whole plastic track system is worn-out and floppy nothing other than a complete new system is going to cure it!

Not having a new tank to compare with makes evaluating the track system impossible.

Thanks all for your help.