With respect to royalty, which of the kingdoms of ancient U.K ( England and Wales) had the greater royal power

In Anglo Saxon England there were seven Kingdoms that had a significant amount of power: East Anglia Kent Mercia Northumbria Sussex Wessex Essex. They all had periods of dominance but in the 8th century Mercia became the dominant Kingdom for almost 100 years. It was supplanted by Wessex who eventually came to rule the whole of England. The current Royal family is decended from the royal family of wessex.

ENGLAND

Wales

Well it wasn't the UK back then, each was a separate country and not really united but England was the most powerful.

Probably Wessex had a great deal of power, as it was the closest to the continent and as such other kingdoms had to pass through it to trade with other countries.

I do not really know the different kingdoms from anglo saxon or celtic times. But yeah, compared to today they had more power.

I imagine the romans had the most power in ancient UK , the other kingdoms may have a short periods of dominance, the Church had a strong influence and in a way ruled as well.

The Great Britain did not exist until 1603 when the Scottish King James took the English throne and joined both countries. There was no ancient UK as 'The UK' is a modern term. I am only familiar with English Monarchs from 1066 before that I do not think historians can be too clear on highest power as its the stuff of legend. Tribes etc.