Wirral and Merseyside
Although Birkenhead was already correctly in Category "Wirral" I also added it to "Towns and Villages in Merseyside" (Like Wallasey). This may seem like duplication, but it isn't.
The Wirral category could contain towns like Neston which are not in Merseyside, so it would be wrong to put the Wirral category inside Merseyside for example, since geographically it covers just more than the metropolitain borough and therefore potentially could contain towns outside Merseyside.
So I would suggest that towns that are in the Metropolitain borough of Wirral can go in both Wirral and "towns and villages on Merseyside".
Towns which are in Wirral, Cheshire can go in both Wirral and Cheshire.
This should allow all local town/village categories to be found by anyone.