As long as you don't change the structure, (ie move walls put in a new door way,) and it was already a dwelling then it you are allowed to restore it, putting in windows, doors etc without getting the OK from building regs.
But if you wanted to put in a wood burner, your chimney and vents would need to be up to scratch, you might need to put in a fire exit, and as soon as you start messing about with anything, the whole place would need to be up to date (disabled access to the toilet
)So you could do it but you couldn't make it very modernised at all, you might need to cook on an open fire.
