There are lots of problems with this, not least of which is that neither "Celtic" nor "Germanic" are religions. First, be aware that there are huge gaps in our knowledge about the pre-Chrisitian religions of all of these regions. From what we do know, though, we can tell that they were very different. The idea that there's some kind of pan-Celtic religion that every "Celt" practiced is something that modern scholars have discarded more or less wholesale - why would someone in western Ireland and someone in northern Turkey, separated from each other by countless miles and centuries, surrounded by and exchanging ideas with different peoples, practice identical religions? The form of "Celtic" paganism practiced in Wales seems to be markedly different in many ways from that practiced in Ireland, for example. That's as we should expect - they spoke different languages and had different social structures. Ditto Anglo-Saxon paganism and, say, Scandinavian. From his appearance on Anglo-Saxon genealogical rolls, for example, Woden seems to have both eyes, whereas the Icelandic Oðinn's having only one is a prettty major myth. Then there's the problem of ethnicity. Just because someone was genetically "Celtic" doesn't mean that they worshipped the "Celtic" gods, as genetics are no indicator of culture. The first chapter of Hutton's Pagan Britain gives a good overview of this particular issue, and that book as a whole would be a useful source for you.

There are some other pretty big issues here, too. Why are you classing Scotland as Germanic rather than "Celtic?" The name "Scotland" comes from the Gaelic Scoti who came there from Ireland. Previously what is now Scotland had been ruled by the Picts, about whom we know very little, and their religion even less. And Northern Ireland...woo. Ireland wasn't ruled, in whole or in part, by the English until long after everyone involved was Christian. Then there's the huge geographic areas and sweeping time period we're talking about, combined with the cultural uncertanties I mentioned above - the Belgae, who were living in southern England by Caesar's time, who ancient geographers distinguish from both the Celts and the Germans and who (per Maurits Gysseling) might have, at least originally, spoken a language belonging to a totally different branch of Indo-European. It's not safe to assume, therefore, that they worshipped either the "Celtic" or the "Germanic" gods.