DAMP CONCRETE FLOOR

A couple of weeks ago we could smell damp coming through the kitchen floor. We have wooden floor boards with a concrete slab about 10 inches below this in our 1958 bungalow. We cannot find any obvious leaks. After lifting some boards we found the concrete blow is damp to the touch and smells musty although no signs of mold etc. I have been told that if the membrane has degraded we may have to remove all flooring and dig up the whole concrete floor etc. We have been told the insurance won't cover this as it is a wear and tear. This would cost 1000's of pounds so obviously not feeling too good at the moment. Can anyone offer advice and confirm digging everything up is a possibilty or is there an alternative. Thanks in advance.

have you checked to see if the air vents servicing the floor void are clear?

Thanks for the reply. I cleaned all the vents about 3 months ago. There are also lots of vent gaps in the bricks that hold the joists up in each room. We only noticed the dampness in the last few weeks, when we noticed a quite strong musty smell. The actual damp area I estimate is about 35 - 45% of the whole house area. Only one side of the kitchen (main damp area) has an outside wall and this is a lean to/conservatory that has been there for 30 years or so. The floor has been perfectly dry until recently ?
Andy

Sounds like a leak to me. Damp doesn't come on suddenly like that. Are there any pipes under the concrete?

Thanks for you reply. The mains water pipe coming in is above the concrete. I have checked most of the other pipes but some are not accessible as I have put down wooden flooring recently in 3 rooms so taking it up was the last option, although any other outcome is better than membrane failure. My wife has reminded me that we did have a musty smell in another room at the other end of the bungalow last year, although this one is completely dry this time?