This sort of question invariably generates all sorts of half-truths and misinformation. As usual, there is too little information to make a definitive reply so all one can do is to make certain assumptions and present the relevant options.
Assuming that the questioner is seeking to obtain a JAA licence issued in the UK and that the CAA have not made yet another cock-up in LASORS, the following options, dependant on experience, are currently available:
1. ICAO ATPL with less than 1500hrs valid multi-pilot experience - Complete approved theoretical knowledge training at the discretion of a Head of Training and complete all 14 theoretical knowledge examinations
2. ICAO ATPL with more than 1500 hours valid multi-pilot experience - Complete all 14 theoretical knowledge examinations with no requirement for approved theoretical knowledge training (Note: The CAA assessment quoted by African Drunk is not required in this case but relates to Option 3. below)
3. ICAO ATPL with more than 3000hrs experience in public transport aircraft over 30,000kg MTWA on scheduled international or similar routes, including a minimum of 1500 hours as Pilot in Command (Captain) - Apply to the CAA for reduced requirements for theoretical knowledge examinations (Note: This option will result in a licence endorsed for use only in UK registered aircraft and may not be recognised by other JAA member states)
It is unlikely that Option 3. will survive the takeover of JAA licensing by EASA as it is not compliant with the requirements of JAR-FCL 1.