Was a writer of M1 , M2 , and M3 a British person
SELECT count(*) WHERE {
?x0 a ns:people.person .
?x0 ns:film.writer.film M1 .
?x0 ns:film.writer.film M2 .
?x0 ns:film.writer.film M3 .
?x0 ns:people.person.nationality ns:m.07ssc
}