Can anyone advise some likely candidates for this functionality ( ie a tool which enables management of test plans & scripts and defect reporting)? I am looking for something which integrates these functions and which will enable the tester to raise faults or queries on Testplans/ scripts/ business specs, as well as defects 'Bugs' in the software being tested.
Test Director is the best thing for you to use. But, it will cost you (A lot!). Before you get it have Mercurcy Interactive give you a demo first. Test Director has a lot of "Bells" and "Whistles" to it but you may not need all of that stuff for what you need it for.
Rational ClearQuest(defect tracking), Test Manager, and Rational Robot all integrate to form a unified test management/ tracking solution. however, getting all the tools might be expensive. check out www.rational.com