Every UK citizen is entitled to a living by their own labour
A UK citizen maybe called up to fight to defend the country - this gives them a right to a share in the land we stand on.
The UK is about 60 million acres, there are about 60 million UK citizens - so each UK citizen is nominally entitled to one acre of land.
Farming 6 acres can provide self-sufficiency for 6 people (without huge physical effort) - so each citizen has the (theoretical) ability to be self-sufficient by their own (relatively light) labour. In practice not all land can be farmed, but I haven't included the sea and fishing resources so I am still comfortable with the principle.
This gives a nominal default condition for UK citizens and the ownership of the land they stand on.
It is this that, I believe, should be the logical underpinning of a citizens income and citizenship itself - the right for each UK citizen to the use of, or receive rental income from, a nominal acre of UK land. This is in return for being prepared to defend the country, this should be as of right and untaxable.