A British Cultural Value?

In the wake of the recent death of Margaret Thatcher: "Don't speak ill of the dead?"
 
http://www.guardian.co.uk/commentisfree/2013/apr/08/margaret-thatcher-death-etiquette

and here: http://blog.foreignpolicy.com/posts/2013/04/08/britain_debates_is_it_ok_to_celebrate_the_death_of_margaret_thatcher