query: PREFIX wikibase: <http://wikiba.se/ontology#>
  PREFIX wd: <http://www.wikidata.org/entity/> 
  PREFIX wdt: <http://www.wikidata.org/prop/direct/>
  PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
  
  SELECT ?prefix (COUNT(DISTINCT(?brit)) AS ?number) WHERE {
    ?item wdt:P1417 ?brit
    BIND (strbefore(?brit,'/') AS ?prefix)     
  } GROUP BY ?prefix ORDER BY DESC(?number)