Mr Nutt, No the constitution of the United kingdom is referred to as unwritten as there is no one document that sets out ones rights and obligations nor the role of the queen and parliament or even the existence of a cabinet. this can be contrasted with the US constitution or the French. Instead we have a body of case law statute and parliamentary convention. The fount of all knowledge Wikipedia, states:-
"The constitution of the United Kingdom is the set of laws and principles under which the United Kingdom is governed.
Unlike many nations, the UK has no single core constitutional document. It is therefore often said that the country has an uncodified, or de facto constitution.[1] However, much of the British constitution is embodied in the written form, within statutes, court judgments, and treaties. The constitution has other unwritten sources, including parliamentary constitutional conventions and royal prerogatives.
The bedrock of the British constitution has traditionally been the doctrine of parliamentary sovereignty, according to which the statutes passed by Parliament are the UK's supreme and final source of law.[2] It follows that Parliament can change the constitution simply by passing new Acts of Parliament. There is some debate about whether this principle remains entirely valid today,[3] in part due to the UK's European Union membership.[4]"
Many think that a single codified document would help others fear it gives the likes of the freemen more grist to their mill.
You will note the constitutional doctrine of parliamentary sovereignty completely trumps the freemen's contractual argument.