Say you are routing Elstree to Bembridge (assuming it's back in action!), via somewhere near Booker to make the turn south but in any case avoiding LHR class A. All in IMC but out of airways and no GPS just standard VOR/NDB/DME.
Don't even think of it without GPS and radar cover. In theory you could fly VOR radials off CPT and SAM but I woudn't recommend it unless you were desperate.