I came across a truly puzzling claim in David Rogers’ new book about the Privy Council:
At perhaps the most mundane and perfunctory level, every time a Bill completes its passage through the Houses of Parliament…it cannot become law as an Act of Parliament until it is signed by the Queen in the presence of Privy Counsellors. This goes back to the time when Parliament did not trust the monarch and thought it at least a possibility that the Sovereign might ever so slightly change the wording.
This was the first time I’d heard anything about the Queen having to grant Royal Assent in the presence of Privy Counsellors, and I was immediately skeptical. At first glance, it sounds plausible, but it’s unlikely to be true.
The signification of Royal Assent is governed by the Royal Assent Act 1967. It established a simplified procedure where the Queen grants Royal Assent by signing Letters Patent under the Great Seal of the Realm, and this fact is notified to both Houses of Parliament by their respective presiding officers. This supplanted a more cumbersome practice where Royal Commissioners acting on the Queen’s behalf signified Royal Assent in the presence of both Houses of Parliament.
There’s nothing in the Royal Assent Act that says that the Queen must sign the Letters Patent in the presence of Privy Counsellors. It’s difficult to imagine how such a requirement would work in practice. As far as I’m aware, these Letters Patent are submitted to the Queen in her red boxes like any other official document that requires her signature. Arranging for Privy Counsellors to witness her signature would be quite burdensome. Although certain members of the Royal Household are Privy Counsellors (e.g., the Queen’s Private Secretary), as are the Duke of Edinburgh and the Prince of Wales, it seems highly unlikely that they would be called upon to act as witnesses.
The stated rationale for having Privy Counsellors observe the signing also seems specious. Originally, the Sovereign granted Royal Assent in person in the presence of both Houses of Parliament. However, they never actually signed anything. Instead, a clerk read the title of each bill, the Sovereign gestured to signify their Assent, and the Clerk of the Parliaments declared the appropriate Norman French formula. Surreptitious editing would have been extraordinarily difficult. Also, membership of the Privy Council was originally conferred at the Sovereign’s sole discretion, so it’s unlikely that Privy Counsellors would have been called upon to hold the Monarch to account in the way that Rogers envisions.
Rogers doesn’t cite a source for his claim, so I’m not sure where it came from. He may have been mislead by the fact that certain types of legislation do receive Royal Assent at a meeting of the Privy Council. For example, legislation from the Channel Islands is approved by the Queen-in-Council, as were Measures of the Welsh Assembly. But none of this applies to Acts of the Westminster Parliament, so Rogers is mistaken.
 David Rogers, By Royal Appointment: Tales From the Privy Council, the Unknown Arm of Government (London: Biteback Publishing, 2015), n.p.
 The old procedure was time-consuming, and MPs resented the fact that they had to drop everything and walk over to the House of Lords whenever legislation needed Royal Assent. The old procedure is still used, but only at the end of a parliamentary session.
 The Welsh people voted in 2011 to increase the Assembly’s legislative competency. As a result, the Assembly gained the power to pass Acts instead of Measures, and they receive Assent by Letters Patent like Acts of the Scottish Parliament.