It turns out that UK Parliamentary constituencies are not well represented in Wikidata; for example many lack details of adjoining constituencies, coordinates, and shape files.
A query highlighting the missing data, and a tool for finding neighbouring constituencies, can be found at:
https://www.wikidata.org/wiki/Wikidata:WikiProject_British_Politicians/Const...
with discussion on its talk page.
If you can help with improving these items, please do!