A possible way of finding out (although they may charge I think) is with the Open University at:
Credit Transfer - About Credit Transfer
I was awarded 120 points at level 1 on the basis of a Master Mariner Certificate but this involved a cumulative college study of 18 months whilst gaining the two lower level certificates first as well as a further six months for the Masters. By comparison the ATPL writtens took a 7 week full time course (very good course though) so I don't anticipate that they would award the same amount but may be worth a go. Good luck.