Prick damsons all over with a fork.
Put into a glass, ceramic or stainless steel vessel with the vinegar and steep for a week, stirring every day.
Strain through a muslin cloth (or a bit of clean, plain net curtain).
When ready to bottle.
The bottles and tops need to be cleaned. (sterilize the plastic tops using boiling water). The bottles must be hot, to avoid them cracking when the hot vinegar is added. (Stand them on a baking tray in the oven and heat at 1000C for 20 mins)
Put the liquid (it should be 3-4 pints) into a large stainless steel pan and heat.
Add 1 lb of white sugar (or as much as you like, to taste) and stir until the sugar is dissolved.
Bring to the boil and simmer very gently for 15 mins.
It is then ready to bottle it.
Once filled and sealed, leave to cool, then store upright in a dark, cool place.