Laying Flagstones onto concrete floor in black and white cottage

Hi

We live in a black and white cottage and about 40 years ago the previous owners dug up all of the flagstone and dotted them around the garden and stuck them on the fireplace!!

They laid down a concrete floor over soil and a dpm made of plastic - there may be some sand amongst the soil. We laid down carpet 20 years ago but are now considering laying down flagstones. We have been quoted a horrendous amount of money to dig the floor up - across the lounge, hallway and dining room, suggesting digging down 1 foot and then insulating etc and then laying down underfloor heating and flagstones. However, it has been suggested to us that we could screed the existing concrete floor as there is no damp and then lay the flagstones on top. What would your advice be? We cannot afford the disruption of digging up the floor or the expense and if this were the only option we would have to give up and revert back to carpet or Karndean Art Select limestone effect floor tiles.

I look forward to hearing from you asap

Kind regards
RV