Peg, I've got the Maltwood book, and read it some time back. I know that there are supposedly zodiacs elsewhere in Britain as well (no, not where I am at the moment).
My feeling is, based on the following, that the idea probably is supporting more than it can, that it is a sort of Tay Bridge hypothesis.
1.That the inhabitants of this island, at the time required, could not be shown to have the same sky patterns as the Middle East. Other areas see the sky differently, so it's unlikely that they were the same. I know Maltwood makes some variations, but they don't seem to be based on looking at the sky first, which they would need to be.
2.Some of the patterns depend on field and ditch patterns which postdate antiquity - perhaps being as recent as the 17th century. They are to do with the major drainage of that period - very straight-lined, not following natural features, or related to known ancient settlements.
3.Some of the areas would have been under water at the required time.
4.Britain has a vast plethora of ancient and not so ancient features which could be used to plot out patterns anywhere you wanted. I have tried various patterns in various places, through the process, I will draw a (insert geometric pattern, animal image, whatever) around (insert whatever placename comes to mind), and succeeded, sometimes with better results than Maltwood. Some of these successes may not be entirely random, so I will have to try again, randomising the process better, and I am certainly not telling anyone what I found, in case it starts off a wild goose chase. OK, may be I'll try that. A wild goose around or near, Harrogate. (First British placename found in a book I happened to open).
5. The human brain is designed to find patterns in its surroundings, and make sense of very few clues. See :) for confirmation. Smother it in the information on a map and it will attempt to simplify it by turning it into pictures. That's why there are constellations in the first place.
Those things being said, I wouldn't want to rule out that there might be, in some place or other, some representation of something or other that might be somewhere up in the sky. But we're more likely to find it by getting a good star map that accounts for the apparent curvature of the sky, removing all the lines that outline the constellations, making sure that it only shows the stars which could be seen by the naked eye in the place and time under consideration, and then looking for the really obvious patterns. Orion (see above), the Plough (Big Dipper), and Cassiopeia are strong candidates, as is Cygnus, and in some places and times, the Southern Cross. Some of the zodiac signs are really hard to distinguish. Then see if any of these patterns fit with anything the locals might have wanted to know, like times of harvest, or floods or whatever, and finally, remember that Britain is not a good place for astronomy, and given the fertility of the past, wasn't any better then. Like Ireland - we are green because we are wet - clouds rule the British skies, not the constellations.
I remain to be convinced.