Hi TamzNo, you need an NVQ and experience
As you so often keep me up-date, I for once can return the favor, the City & Guilds 6189 Diploma Level 2 & 3 is the replacement qualification for the old 6129 Tec Cert & 6089 NVQ the idea was to combine both the college & on-site stuff to stop training centers just offering the off the job training which was not recognized as being a qualified plumber by the industry.
Unfortunately they seem to have bowed to pressure & now also offer the 6035 (just the college side) so the confusion will still continue hear in England.
So just to confirm the 6189 Diploma contains on-site assessments which have to be completed to pass the qualification & so effectively replaces the old 6089 NVQ.
Experience is of course always required to be able to work as a plumber, the problem as you know, is how do we measure it !!