So many errors and inaccuracies on this thread that it's difficult to know where to start....
IMC Ratings: Valid only in UK airspace. The old UK CPL and UK ATPL had IMC privileges equivalent to the IMC rating which were valid as long as the licence was. The JAR-FCL CPL and ATPL have no such privileges.
IR: Entirely separate to a JAR-FCL CPL, UK BCPL or UK CPL. There is no requirement to hold a ME Class Rating or ME IR on any CPL; however, the theory exams appropriate to the IR will only be valid for 36 months after passing the last exam. In other words, if you pass the CPL exams and obtain your CPL, you then have up to 3 years to add an IR. To keep the cost of licence and rating issue down, many people complete requirements for both CPL and ME Class Rating at the same time and then take their IR on the same ME aeroplane.
ATPL: The JAR-FCL CPL/IR is not 'automatically upgraded' upon achieving any specific total flight time. Most people take the ATPL exams rather than the CPL exams in order to suffer the misery only once, achieving a 'CPL with ATPL knowledge' which is commonly - and wrongly - referred to as a 'Frozen ATPL'. This ATPL theory credit is valid for 7 years from the date of the most recent IR revalidation so long as the first IR is passed within 3 years of passing the JAR-FCL theory exams. There are a number of other requirments for a JAR-FCL ATPL including a ME IR, completion of an approved Multi Crew Co-operation course, 500 hours multi-pilot (not multi-engine!) time and a minimum of 1500 hours.
Finally, if you hold a UK rather than JAR-FCL professional licence, remember that there is no necessity to convert to a JAR-FCL equivalent! Which means that even Restricted BCPL holders can continue to have their licences re-issued upon expiry.