Complex sentence: National referendums can be permitted by a Act of Parliament they are by tradition extremely rare due to the principle of parliamentary sovereignty meaning they cannot be constitutionally binding on either the Government or Parliament although they will usually have a persuasive political effect.
Split into simpler sentences: National referendums can be permitted by an Act of Parliament, although they are by tradition extremely rare due to the principle of parliamentary sovereignty. This means that referendums cannot be constitutionally binding on either the Government or Parliament, although they will usually have a persuasive political effect.