I've done a bit more routing around and whopity seems to be correct, although I suspect that if you are in the process of applying for jobs having a JAR licence is presumeably going to help. (unless you limit yourself to UK)
If you are in a steady job there's probably no point in changing anything. I now have it from the CAA that ATPL exam credits for those with UK CPL (fATPL) will continue to be valid until at least 2012, possibly longer.
You can have two licences but will have to pay twice....