I'm renovating an old cottage with ragstone dividing wall to next house. There's no evident damp or humidity problem.

The walls are built with lime mortar joints and what's close to mud internally (?)

I'm thinking of lining the internal kitchen wall with OSB so that I have better fixing for wall cupboards.

Any advice welcome - should I put a vapour barrier behind.

If the wall is nice and dry the OSB should be fine.  I would not bother with a vapour barrier as I am not sure what vapour flow you would want to stop.  They are often used on the warm side of insulation to control warm moist internal air from condensing in the insulation or the structure but this is not what you have as it is an uninsulated party wall.

Ok, that is what I had thought, just wanted other opinions