henry zeffman
chief political correspondent

The debate secured by the Liberal Democrats this afternoon is very specific.

Sir Ed Davey is seeking the release of documents relating to the appointment of Andrew Mountbatten-Windsor, then Duke of York, as government trade envoy in 2001. It is also seeking a letter from Peter Mandelson expressing his views on the appointment.

But Mr Davie and the Lib Dems have made it clear that they have a broader aim in calling for this debate.

Announcing the motion, Davie said: “Regardless of title or friend, no one should be above parliamentary oversight. It’s time to end the era of impunity.”

In other words, today’s debate aims to demonstrate that Parliament in general, and the Liberal Democrats in particular, will scrutinize even the King’s younger brother.

However, there are restrictions on what can be discussed later. Under House of Commons practice, MPs are expected to avoid criticizing any member of the royal family other than Mountbatten and Windsor.

And while MPs have the privilege of defending what they say in the House of Commons today, they are likely to be warned by the Speaker that they risk harming the police investigation into the former Duke of York.