Thanks for all the replies folks, for the meantime, a quick and cheap fix is being made. 4 x 1000 litre cubes linked in series with alcathene pipe which will fill from the ditch, hopefully before it runs dry.
Declan, a very kind offer indeed, I'm in Clackmannanshire near Dollar.
Another problem is that the land is off grid so an electrical submersible pump may not be an option unless I also get a wind turbine. This could be a costly idea!!