not really., as far as is known. the britons were subdivided into smaller kingdoms until the roman conquest, so even cymbelline and his freinds only ruled part of it. There were celtic rulers of smaller kingdoms in england though
you mistake the way that the romans did business- they ran small cclient districts in britain that retained their local king. which is why boudicca was still around after the roman invasion to lead her rebellion. And if you think about it most of those kingdoms, like wessexc and mercia were largel;y saxon or anglic. the celts were well marginalised.