paco - what you say is correct for ab-initio cpl/atpl, but article 8 allows for a reduction in training for icao compliant foreign licence conversion which is what the OP is talking about.
It's in CAP804 - Section 4 part Q - but to paraphrase - foreign ATPL holders with a valid type rating are given full credit for training and thus do not require any mandatory theory course or indeed formal flight training and foreign CPL holders may have their training reduced by the theoretical knowledge provider.