An interesting test to see how many of these guys were "passports of convienience" would be to see whether they "went home" after retiring:
e.g. Tony Greig - chipped off overseas ASAP
Robin Smith - stayed with Hampshire, lives down there, helps run day to day operations, helped set up Chase cricket equipment
Chris Lewis - Firmly in Blighty at Her Majesty's Pleasure etc. etc.
How many off them return from whence they came? If they stick around in the UK, were they really playing for England out of convienience?