Insurance aspects of window replacement - advice needed!

[Sue]

My bay has subsidence, has had resin injection and now has to be rebuilt.

At the start of all this, and before I knew that the bay would have to be rebuilt, I told the insurance company that I intended to take the opportunity to replace the existing single glazed windows with double glazed ones.

The insurance company said that they would pay for the labour in replacing the windows, since they would have to pay for replacing the original windows anyway as part of the work, but they would not pay for the actual windows as the existing windows have wear and tear and the policy doesn't cover that.

I was originally told the building and redecoration work following the resin injection would take three days. This has now turned into six weeks after the builders turned up and went away again and a second surveyor turned up with profuse apologies. It transpired that the initial survey done was not done properly, and the person concerned has left the company.

A stone mason has now become involved, as well as the builders.

As part of the revised work, the existing windows still have to be removed, BUT apparently could not be replaced anyway as they won't fit in the new gaps after the rebuilding.

Also, apparently at least two of them are likely to disintegrate on removal (though on prodding them they seem pretty sound to me).

Now ......

Had it not been for the subsidence, I would not be replacing the windows. If I was keeping them, I would just get any iffy bits repaired and the frames repainted. There would be no question of disintegration on removal, as they would not be being removed.

Surely if they will not fit back into the wall because the gaps will have changed after the rebuilding, that is a direct result of the bay having subsided and the actual windows should be replaced by the insurance company?

And my son-in-law says that replacement windows these days have to be double glazed, under building regulations (or something).

Can anybody advise? I don't want to approach the insurers (it's actually Cunningham Lindsey I am dealing with, not the insurers directly) unless I am sure of my ground.