Every time l slow down using engine breaking on my 206 l get a repetitive tapping/knocking noise from the engine or gearbox. It is worse when slowing from high speeds (as it would be!). The noise then subsides when l engage the clutch but returns as l come off the clutch again. Any help?

Does it make a noise at standstill then stop when you press the clutch? If yes its your thrust bearing. Other than that you need to take it to a garage and let them listen to it.

l was thinking 'thrust bearing' too, BUT this is usually a whirring, light grinding noise.from the spinning nature of the bearing.
NOW, l think that it is ur inside driveshaft joint. NOT the outer CV constant velocity joints, they make knocking noises when rounding a corner.
But the inside joints, when under power from the gearbox, will make noise upon acceleration, or deceleration.

Another 'joint' on the 206, is the 'intermediate bearing' on the right side driveshaft. It allows the longer right side driveshaft to make a slight 30 degree bend from gearbox to wheel CV joint.
A trained ear (in ur city) can hear the difference.