Update - looked like the bicarbonate/ vinegar and later drain cleaner worked, but it hadn't. Had another look outside and lifted the drain hole cover - the outside drain could be seen (the one above ground must be the original one) so bought a cable tool from Screwfix which went right through to...
Thanks, PullerGas. I've used bicarbonate of soda and vinegar, then hot water and plunger. This seems to have worked so will try it out later. Thanks again to all. Chris
Thanks for all your advice. There isn't an external wall pipe - it sounds like the water goes into the the toilet waste pipe. The bathroom is fully tiled. We tried a plunger but don't want to chance soda. Have attached another image without water to see if anyone has seen one like this before...
We have the same problem but cannot access the other end of the drain or under the shower tray so need to try and open the waste trap to clear out the blockage. Could someone please explain how to do this. Thanks