Thumping/knocking noises from under car

this may be exhaust moving best thing to get in garage an let them take a look most garages do for free.

You dont say if noise is coming from the front or rear .If from front , common cause is anti-roll bar link arms .

Many thanks for your suggested causes - not quite sure if knocking noise is from front but thanks for suggestions that it could be caused by loose anti-roll bar +/or exhaust system ... I will definitely get these possible faults checked out at local garage asap.