Leigh Sinton way?
Basic rule of thumb for Worcestershire
£10-15k per acre for pasture/utility land, for plots of 3+ acre
However, you are v unlikely to either a) buy a plot that stands much chance of PP for housing for anything like pasture prices or b) do so without a hefty overage clause on it for when you do get PP.
Self build plots are in the order of £100-200k depending on location and size of PP.
Method of finding land value, very roughly, is
House Price value (say £400 k for 4bed/1,500 sq ft in Leigh Sinton)
Less £150 psf build price (£225k)
Less 20% profit (say £60k)
= Land value (£115k) say.