Nuneaton has two roofing populations and the wrong assumption about which you have is an expensive one.
The Victorian and Edwardian housing is largely slate on cut timbers, built in long terraced runs with shared party details and valleys where the rows meet. Those junctions are where the water gets in, and a valley patched for twenty years will keep failing at the same point until the lead is renewed properly.
Chimney stacks deserve particular mention on this stock. On a terrace the stacks are shared, exposed on every side and usually still carrying original flaunching, and once the roof around a stack has been patched a few times the stack is generally next. If scaffold is already up for a re-cover, dealing with it then costs a fraction of bringing scaffold back in three years.
The interwar, post-war and modern housing is concrete tile on trussed rafters. The weight point runs the other way here: a roof built for concrete tile will generally take slate, but a roof built for slate cannot always take concrete tile, because concrete is heavier. If somebody offers to re-cover an old slate roof in concrete without looking at the structure, get a second opinion.
Re-covering triggers a Building Regulations requirement to look at insulation, and we arrange that inspection and see it through to sign off. More on our roofing page.