Yes, the foundations of the constitutions are not the same, one of them has a mostly codified constitution, the other has a mostly uncodified (uncodified but mostly written down, that is not a contradiction!) constitution. They both have constitutions however, so the phase "Britain has no constitution" is wrong. To be clear, I am not saying that is good or bad that Britain has an uncodified constitution, just that from my definition (and most political and legal definitions) of what a constitution is the phrase "Britain has no constitution" is wrong. Britain of course has laws, and laws about how new laws are made, etcetera. This forms a constitution.
I think you have diverged too much...well from reality, in order to try to prove a point. Do you think most people, or lawyers, or judges in the UK spend their time trying to enumerate all the laws of the land before they proceed in their court cases? Do you think that people think that the UK system of government is illegitimate? What point are you trying to make? Because it is not grounded in reality. You can debate the merits of a codified constitution versus an uncodified one, but the UK does have a constitution, the vast majority of which is codified into many documents. The following two links might help you:
I believe interpretation is a part of the definition of a constitution, you do not, we have different definitions, oh well. I also believe the uncodified/codified distinction is not binary, it is obvious that the US constitution is far more codified than the UK constitution, the two are at opposite extremes.
I find it weird that people would downvote this, I know you should not complain about it, but this comment is correct. The UK does have a (uncodified) constitution. Also of note; even countries with a codified constitution have parts that are uncodified.
The UK has an extremely entrepreneurial culture as well, which is shown in the data (number of businesses registered, number of startups, both per capita), it ranks very highly, along with other indicators of innovation, it might not be as entrepreneurial as the USA, but globally it ranks very highly. The fact that you mention the Soviet Union and its central planned economy and the (outdated and stereotyped view of the) British class system almost like they are equivalent really undermines your point as well.
Other's have mentioned that Forth isn't an esoteric language, however if you want a Forth written for an esoteric language I have written one for SUBLEQ (see https://esolangs.org/wiki/Subleq). Although SUBLEQ is more of an esoteric machine than a language, it also sort of qualifies as one (and has an entry on the esolangs Wiki).