What makes you think any of this is 'unlawful'?
Obviously under our political system the government can legally do whatever it wants if it can get a law through Parliament to say so, but to achieve that they'd have to be open about what they're doing and convince enough MPs and Lords that it's justified.
[1] https://digital.nhs.uk/about-nhs-digital/our-work/keeping-pa...
Then presumably they're relying on GDPR points 9(2)(h) and 9(2)(i) with reference to that national law to argue that the default prohibition on processing health data in paragraph 9(1) doesn't apply.
And then they've got public interest/official authority under 6(1)(e), or perhaps compliance with a legal obligation under 6(1)(c), as a lawful basis.
But all of that just means the processing wasn't automatically prohibited under the GDPR. All the normal rules including the principles set out in Article 5 still apply as well, and those principles include purpose limitation, data minimisation, storage limitation, and integrity and confidentiality. There are also some specific obligations around professional secrecy under Article 9 because it's health data.
Given the extremely broad scope of the intended data lake here, the ambiguity about who might end up with access to it, and the extremely sensitive nature of the data, I don't think I'd want to be the one defending NHS Digital when the seemingly inevitable ICO investigation comes.