If you have lat/long this formula gives a good approximation to the distance between two points on a sphere

d = acos(sin(lat<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">1</SUB>).sin(lat<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">2</SUB>)+cos(lat<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">1</SUB>).cos(lat<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">2</SUB>).cos(long<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">2</SUB>−long<SUB style="POSITION: relative; LINE-HEIGHT: 0; BOTTOM: -0.25em; FONT-SIZE: 0.75em; VERTICAL-ALIGN: 0px; TOP: 0.8ex">1</SUB>)).R

Where R is the radius (typically 6371km for the Earth)

Dont forget you will have E and W longitudes in the UK so you need to take that into account by converting them into angles that mean something in the above formula