Keith I take it that your reference is to DD and not DDX. The link certainly is to DD. However I tried to recall ever seeing it on any retailer websites, couldn't and so checked but failed to find it.
I then tried Harman Express and there was no mention of it. Putting in a search only got me to DDX although clearly DD exists. However the tech specs for it only seem to cover large capacity dip and dunk and all temp refs are to mid 70s F.
Maybe it isn't generally available to home darkroom users?
Do you know where it can be obtained and in what size containers?
Maybe it is a special order item, but it's listed on Ilford's website.
Simon Galley would know for sure.