I agree with all that has been said especially B.J.Leneham. However one thing to consider
is that it does not apply to the backing on wallpapers such as vinyls where you can strip the top
layer leaving what looks like a lining. This is not suitable.
This definitely needed removing and the wall prepared and re lined.
Lining paper correctly applied is the proper base for wall papers, in fact the more expensive
wall papers require a lining and this is invariably a cross lining (horizontal) this gives a
In your case I assume that the lining paper has already been emulsioned. If this is the case
it needs a coat of sealer. personally I use a paste like solvite with pva
added. This will then seal the wall, and as others have said you can stick edges tackle bubbles
etc. at this point.