The Cathaginians never seem to have ruled all Spain – only the coast. The earliest historical record we have of a majority population is of the Celtiberians, related to the Gauls, although there are archeological records of an older Iberian culture, with a language that does not seem to be related to any known language. (I cannot find an explicit statement that this includes Basque, but seeing that I find the two listed right next to each other on a list of language isolates, I can only assume that it’s been tried.)
This is all uncontroversial stuff you can find in the Britannica, etc…
Britany is called “Britain the Less” because British refugees from the Saxon invasions settled there starting in the 5th century. The people there still speak a Celtic language related to Welsh and Cornish, despite many years of persecution by the French.
On another subject, although the union of England and Scotland is the long-term result of King James VI of Scotland inheriting the English crown from Queen Elizabeth I of England, and becoming King James I of England, the actual Union of the Parliaments, a hundred years later, was definitely an English takeover of Scotland. Until then, they had simply been two countries with a shared monarch. Scotland had just been thoroughly Enroned by a scheme to start a colony in Panama, and needed a bailout, while England wanted to be sure that when Queen Anne died, and King James VI/I’s direct line with her, Scotland would choose the same distant – and Protestant – cousin that England did. So the Scottish Parliament was – ahem! – convinced to vote itself out of existence in return for some seats in the Parliament in London. A few years ago, Scotland got its own Parliament back, although the Parliament in London is still solely responsible for foreign affairs and the military; all along, however, Scotland has continued to be a quasi-independent country with its own laws, no matter which parliament passed those laws.
The original United Kingdom of Great Britain became the United Kingdom of Great Britain and Ireland a hundred years later; at the same time, the Cross of St. Patrick was added to the Union Jack. In the 20th century, it became the United Kingdom of Great Britain and Northern Ireland.