I’m all for a duty of candour on all public servants, politicians and indeed private corporations. If you fucked up you must tell everyone you fucked up including near miss events. A duty of candour for public civil servants in political departments must be separate from that of politicians so that one or other owning a mistake does not relieve the other from having to do so also.
As it stands there is zero incentive for a politician to admit a mistake and little room for civil servants to make such a mistake known.
If I ruled the world (it’s coming :D) I’d pay politicians very large salaries, enough for life in their first term as an MP, but they can never have another paid job again and their bank accounts are scrutinised by a public body for the remainder of their lives and that of their spouses and children for 10 years after they leave office. Thay could take voluntary work but non paid. Of course, the problem is that any system will be open to some abuse.