I can't work out the handle either. It's a socketed axe, so it can be fitted to different hafts, but this seems unwieldy. Maybe it's used for driving downwards, using the weight of the haft?
What a cool find. The Must Farm dig for anyone else interested. I have seen these socketed axe heads in museums but didn't really understand the proportions of the complete tool.
Such unlikely circumstances to burn then extinguish and then preserve this family's possessions for so many centuries.