Theory was first put forward by Montesquieu, French political theorist in 18th century – theory states that there are 3 primary functions of the state, and only way to safeguard liberty of citizens is by keeping 3 functions separate. Power of each is exercised by an independent and separate body, each can keep check on others and limit amount of power wielded by any group. There is some overlap, especially the fact that the lord chancellor is involved in all three functions – this role has been reduced though. Overlap with executive and legislature in that those ministers forming gov also sit in parliament and are active in law making process. Very little overlap between judiciary and other branches, apart from lord chancellor, which means the judiciary can check and ensure executive does not overstep constitutional powers, accordance with Montesquieu’s theory