Damp underlay and carpet

I am assuming you do not have under floor heating. It sounds like high water table problem and you membrane has failed . Water is coming under the property from some where I would check if any rams , slabs, are leaning towards the house . then check all drainage is working correctly . Is the area around you (neighbors house , fields , ) a higher level than you ? If you are the lowest point in the area all water will congregate towards you , you will need to divert this water down a drain or past your property.

Looks Like you haven't got a DPM under the concrete also check for leaks on your radiators to see if the pressure goes down on the boiler if you have any downstairs radiators where the pipes run under the ground .. also this could be groundwater if your levels are low and and also this could be condensation so take your carpet up and see if it dries out if it doesn't it's definitely groundwater and you will need a pump and membrane work if it's just slightly damp you probably got a very thin layer of concrete with no physical plastic damp proof membrane you're welcome

In almost all cases this will be a condition of condensation under the underlay due to a tiny difference in the floor temperatures. An easy test for this is to leave an area of floor exposed for a few days and observe how it dries; if it notably dries its condensation, if it doesn’t , it’s actual water, which can only come from a pipe leak or ground water .

Ideally I would need more information regarding the room mentioned? Concrete slab floor sounds suspect. I would check on plans to see if there may be a drain covered over under the concrete floor or waste pipe. Check if drainage for bath/washing machine or dishwasher is working properly. Do you know where the man hole is? If all ok then look at replacement or fix for damp proof membrane?

Sounds to me that you have an old building probably no dpc Would need two layers of tanking slurry and the self-levelling compound put on top Doesn’t say bungalow or house i.e. bedroom