Hello, I wrote an answer here a little while ago which addresses the how contentious and flawed the idea of the Witan in; to whit, it's largely an invention of Victorian Whig historians who wanted to create a false history of English Parliamentary democracy.

The question boils down to whether or not you mean pre-Norman British Kingdoms or pre-Norman English Kingdoms. By the time of the Conquest of 1066, England had been a unified kingdom for almost 150 years, and working towards unification for over 200. From the 870s in particular, Anglo-Saxon kingdoms tended to be highly bureaucratic and relatively centralised polities with strong social and governmental hierarchies. Territory was organised at the 'Hundred' level, and then at the county level, where it was overseen by - broadly speaking - Ealdormen who owed personal loyalty to the king. A swathe of lesser nobles and community leaders (thegns, hundredmen) and royal officers such as Reeves all then slotted in to fulfil their duties within the system. Royal authority had increased considerably in the late 9th and early 10th centuries, and was built on a combination of land charters and taxation, royally-controlled civic centres, extensive law codes, currency reform and close cooperation with the Church.

If you want a very good, and very thorough look at the functioning of Late Anglo-Saxon England, I very much recommend Molyneaux's The Formation of the English Kingdom in the Tenth Century.