Book 5 is at the editors. It comes in at 100,000 words (nearabouts). I was thinking of splitting the book into two, but didn't want to make you wait. (Like you I want to get onto the next book and the one after that).
The covers should be coming this weekend, and that only leaves the question of when it'll be published. March, definitely (or definitely assuming there are no major changes needed). Two weeks? Perhaps three? It's hard to say. So it will be out in March, probably nearer the end than the beginning.
After Book 5, there's a Book 6. This is a return to Anglesey, and deals with the creation of a functioning state (and the difficulties doing that in a zombopulated world). And then there is a Book ?, definitely titled The End. This may be Book 7. It might be Book 8. I won't know until I get there.
But, though this is the end for this strand of survivors, there are going to be some spin offs. One set in the US, another in Canada, each dealing with different stories that just wouldn't work in a UK setting. (I've also got a few ideas for one set in Tasmania, but let's focus on one book at a time.)
So, Book 5 - coming soon to an internet near you (and available for bookshops to order about a day after that.)