hard work for a 76 year old

On the assumption you mean polythene (actual plastic sheeting) and not landscape fabric or weed fabric, if its been down a while, the soil should be dry and lifeless. If its weed membrane (like black fabric or sometimes, black and shiny with green lines here and there) the soil won't be in this condition, so its not as bad.

You do need to dig it really, incorporating composts, specially if it was covered in plastic, but if you can bear to wait, you can try cheating - you'd have to buy in lots of organic material, such as composted animal manures, or soil conditioning composts (not potting composts), then spread it to a depth of 3 inches over the whole lot and leave it for a year. In that time, life should return to the area and you should be able to plant next year.

Markel, If you find it difficult to do all the digging, or you don't want to wait too long to be able to use the land, then you could get a rotavator and let it do all the work. You can hire electric or petrol powered machines, they don't cost too much to hire, they will do the job in a fraction of the time it takes with a spade and will save your back.

You could also throw some manure, compost or mulch on the top and use the rotavator machine to dig it all in.