In countries with constitutional monarchy, what is the percentage of cities located in the district of England?
constitutional monarchy refers to GovernmentForm = 'Constitutional Monarchy'; percentage = MULTIPLY(DIVIDE(SUM(GovernmentForm = 'Constitutional Monarchy' WHERE District = 'England'), COUNT(GovernmentForm = 'Constitutional Monarchy')), 100)
SELECT CAST(SUM(CASE WHEN T1.District = 'England' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM City AS T1 INNER JOIN Country AS T2 ON T1.CountryCode = T2.Code WHERE T2.GovernmentForm = 'Constitutional Monarchy'