The new Cabinet has been announced. One unusual feature is that the new Leader of the House of Commons, Sir George Young, is to attend but will not be a member of Cabinet. I have not seen any reports of the rationale for this, unless some of the responsibilities are to be assumed by the new Deputy Prime Minister.
The Leader of the House has been an important Cabinet post, the holder being responsible for the management of the Government’s business and chairing the Cabinet’s legislation committee to decide the programme for the new session. The title itself did not become established until the mid-19th Century and until 1942 was normally held by the Prime Minister, unless the PM sat in the Lords.
It could be argued that the difference between being a member of Cabinet and attending Cabinet is not that great, the former having a right to speak and the latter only speaking when invited, but it is an unsual move in a Parliament when business management will enter largely unchartered territory.