Wasn't it called Gypsy Tart? Gary Rhodes did a recipe for it I seem to remember as it was one of his favourites too.
I went to school in Kent and it was called that there as well....../.
I have a school dinners cook book and both butterscotch tart and gypsy tart are listed. one is made with evaporated milk and brown sugar ( gypsy tart) , the other with butter,brown sugar flour and milk (butterscotch tart). I cant imaging the end result tastes much different to be honest, but can give you either recipe, xx