Purpose/Rationale of Conventions (a) They are a flexible means of changing and developing the constitution informally. According to Jennings, conventions 'fill in the gaps' in the UK's constitution. (b) They define powers, regulate the authority of the Crown and underpin the operation of the Cabinet system. (c) They regulate internal relations between the House of Lords and Commons. (d) They also regulate relations between the UK and other members of the Commonwealth. (e) They help to control and provide accountability of the Executive.