How can ministerial aides scrutinise their own bosses?

The newly-appointed PPS to the Wales Office - and member of the committee set up to scrutinise it - Chris Davies MP.

It's a committee that tends to make headlines more for its membership rather than its investigations.

And to the rows about having no women members, a surfeit of Davieses and a Labour MP from Yorkshire we can now add questions about the role of ministerial aides on the Welsh affairs select committee.

Brecon and Radnorshire MP Chris Davies has just been appointed parliamentary private secretary to Wales Office ministers Stuart Andrew and Lord Bourne. He hopes to continue to serve as a member of the committee set up to scrutinise its work. He is not alone.

Montgomeryshire Tory MP Glyn Davies remains a committee member despite being parliamentary private secretary to Welsh Secretary Alun Cairns. His appointment to the committee passed without a political row as he is seen as more independent-minded than the typical PPS.

Parliamentary private secretaries or PPSs are not officially members of the government, although they are on the payroll vote, which means they have to toe the government line in divisions or resign. Chris Davies says he's the first Brecon and Radnorshire MP to be appointed to "government office" since Jonathan Evans in 1997.

You could be forgiven for asking if there are rules to prevent this obvious conflict of interests, to stop members of the government marking their own homework. And there are. It's in the ministerial code. Here's a neat summary of what the code says, courtesy of the House of Commons library.

'Embarrassing'

The library note says: "The code states that although PPSs are not prevented from serving on select committees, they should withdraw from any involvement with inquiries into their appointing minister's department. PPSs should also "avoid associating themselves with recommendations critical of or embarrassing to the government".

If PPSs are expected to avoid associating themselves with recommendations critical of or embarrassing to the government what are they doing on select committees scrutinising the government?

Messrs Davies and Davies are not the only PPSs on the Welsh affairs committee. Simon Hoare, a Dorset MP who hails from Cardiff, has just been appointed PPS to Education Secretary Damian Hinds. At least Mr Hinds is not one of the ministers scrutinised by the Welsh affairs committee, although the "critical or embarrassing" point above still applies.

If this were, say, the Treasury or Home affairs select committee, this would either not happen or there would be an almighty row.

But as this is a committee that shadows a department with few executive powers, a committee that few MPs want to sit on, the presence of (effective) members of the government on a committee that scrutinises the government is no big deal. As one MP put it: "There's Wales for you!"

The Wales Office has been asked to comment.