Somewhere I have a list of things that can be put in references, which can be interpreted more than one way.
“A person like this is hard to find” (ie he’s always skiving off)
“Nothing can describe the contribution he has made to....”
Or for someone who drinks too much:
“I often felt he was wasted in his current role”
“He enjoyed many happy hours while employed us”
and finally
"I cannot recommend this person too highly. If you can get him to work for you, you will indeed be fortunate"
But seriously - what they said above - the DPA may exempt you from being required to provide the reference, but does not prevent the subject of the reference requesting it from the other organisation (whether or not their application was successful).
If asked to give a reference, I will always give a copy to the subject.