Adferiad Recovery Ltd v Aneurin Bevan University Health Board  EWHC 3049 (TCC) is a procurement case in which a below-threshold procurement is challenged on the basis of general principles of EU law. Post Brexit, that is. The judgment is of note for its contrast with Lipton. Particularly  ff are crucial paras, in which Keyser J (in, he acknowledges, some contrast with Lipton) holds that the Withdrawal Agreement implies that general principles of EU law do not ground a cause of action in domestic private or public law.
Lipton on this point ( in particular) implies that all general principles of EU law are part of domestic UK law as a result of the Withdrawal Agreement, provided they were so recognised by EU law on Brexit Implementation Day, and provided of course subsequent UK law has not changed their status.
Should Adferiad stand (which is a big if), EU principles as a result of the WA would continue interpretatively to guide claims made under retained EU law, however cannot by themselves ground such claim. I.e. a claim solely based on alleged violation of EU law principles, fails. The judge in Adferiad takes a more limiting view on general principles of EU law than Lipton where the judge held these are part of domestic law provided they were recognised in relevant case law prior to Brexit completion day.
The case, and the contrast with Lipton, shows the importance of statutory construction of the EU (Withdrawal) Act 2018, and as Jonathan Mills points out, this is in the absence of a constitutional document to provide guidance. The result I fear is a Walhalla of statutory construction which might make lawyers happy, but may leave the subjects of law confused.