Frumpety So what is a constitutional document ? Where would you expect the Coronavirus Act 2020 to be challenged ?
Magna Carta 1215
Bill of Rights 1689
Act of Union 1707
Scotland Act 1998
Human Rights Act 1998
Freedom of Information Act 2000
Constitutional Reform and Governance Act 2010
House of Commons (Disqualification) Act 1975
along with
common law doctrines such as parliamentary sovereignty and judicial precedents, rules of procedure, international treaties and various constitutional conventions.
Not a comprehensive list, but you get the gist.
Where would you expect the Coronavirus Act 2020 to be challenged
Legislation cannot be challenged in the British courts (unlike in other countries with formal constitutions and constitutional courts).
However, decisions based on legislation may be challenged in the courts. That would be the UK courts as well as the ECHR or, for the present at least, the Court of Justice of the EU.