Morgan should be embarrassed and ashamed of the poor quality and/or design of the support for the seat pad. The material used is obviously not strong enough to support the weight of the average driver over a period of time. Here we are talking about 12 years, 80,000km and an 88kg driver. Something left over from an onion bag is no substitute for proper webbing.
I made a temporary "bush mechanic" bodge until I can work out something better. I just wedged in a couple of old bits of wood that were lying around but I suspect that it may slip out of place when I start to drive. If it does I will just have to work out some system to hold it in place. The main problem is that the seat will have to be completely dismantled to fix it and August is the holiday period in Italy so there is not chance of getting any work done.