There should be some stuff in the archives about changing to a UK CPL. Basically allow a year an £10,000! I converted an NZ CPL some time back and it took ages. You'll probably have to do a JAR course which will be even worse (sorry to be pessimistic, but it's not an easy job).
Not sure about the instructor rating, but you'll probably have to do the whole UK course and test.
Try
www.caa.srg.co.uk