Beeline primer &Sealant (Colinton EH13)

High quality sealant, especially good for use prior to wallpapering on old walls.
It went further than I thought and so I've quite a bit left over. I'd say it'd do another 20m sq at least.

It's diluted at 1:1 suitable for non-porus surfaces. For porus surfaces you need to dilute it further to 1:3 so you'd add water to double the current volume.