What would Prince Ernst August of Hanover have to do to reclaim the title of Duke of Cumberland?

Nope

So it sounds like the monarch can, on their own discretion, restore the title.

I don’t think so. The full text of section 2 reads:

Note that wording: “should the committee be satisfied,” then and only then may His Majesty direct the peerage be restored. If the committee isn’t satisfied (and if it never considers the matter, it can’t be satisfied), there’s no other provision of the law allowing the monarch to overturn the decision of Parliament to accept the original list and have them stricken from the Peerage Roll.

It sounds like if the monarch isn’t satisfied or doesn’t want to refer the matter to committee in the first place, then the monarch is not obligated to do so, but in that case, the petition is deemed rejected.

OTOH, nothing would prevent the monarch from giving a NEW peerage title to the current Cumberland and Albany peers. If Prince Ernst August’s son and heir (also, confusingly, named Ernst August, and allegedly legally named Ernst August Prinz von Hannover Herzog zu Braunschweig und Lüneburg Königlicher Prinz von Großbritannien und Irland) married one of the York sisters, for example, the queen could make him Earl of Somewhere or Duke of That Place quite independent of any claim to the Dukedom of Cumberland.

Everyone in that family seems to be Ernst August (or some variant), except for one:

Ernest Augustus, 1st Duke of Cumberland and King of Hanover (1771 - 1851)

George V, 2nd Duke of Cumberland and King of Hanover (1819 - 1878) (the exception)

Ernest Augustus, 3rd Duke of Cumberland (1845 - 1923)

Ernest Augustus, Duke of Brunswick (1887 - 1953)

Ernest Augustus (1914–1987)

Ernst August of Hanover (born 1954)

Most of the oldest sons, anyway; both the current head of the family and his son have younger brothers who are not named Ernst August.

All of the Ernst Augusts of Hanover are nowhere near as confusing as all of the Heinrich Reusses. (Every male member of the Princely House of Reuss has been named Heinrich for eight centuries; the current head of the house is Prince Heinrich XIV, son of Heinrich IV and father of Heinrich XXIX and Heinrich V [they restart the numbering every century]).

That’s about what I thought. Especially given the likely Brexit fallout, it might be a politically-appealing gesture to Germany.

I thought the Queen may grant titles to members of the Royal Family at her own discretion. I don’t recall reading that the PM was consulted before Prince William was created Duke of Cambridge at the time of his wedding, for instance.

I think the Germans would be baffled at the suggestion that they should give a damn about this, frankly.

Couple of problems here. “Royal Family” is a circumscribed class; more remote than the grandchild of a British monarch, and you’re generally not it it. Ernst Augustus of Hanover is not in it. Plus, we’re not talking here about granting a title, but reviving one; there’s no established convention that the Queen may revive deprived titles for members of the Royal Family (not least because the situation has never arisen; not even Ernst Augustus’s grandfather, who was deprived of the title, was considered to be part of the British Royal Family at the time). Finally, established convention always gives way to Act of Parliament, and there’s an Act dealing specifically with this case which prescribes what the Queen may do. She may revive the deprived title if she has referred a petition for revival to a Committee of the Privy Council, and that Committee is satisfied as to certain matters. It follows that, if these things haven’t happened, she can’t revive the title (and couldn’t do so even if Ernst Augustus were a member of the Royal Family).

Except that it would have the Brexiteers frothing at the mouth, which might be an entertaining prospect, but the prospect of HM’s being embroiled in that particular controversy would rule it out. Neither HM or PM want to go there.

But that was expected anyway as customary practice within the family business. What’s being hypothesised here is something unprecedented (always hazardous in this context) that would dust off century-old legislation and bring all sorts of crusty old prejudices out of the woodwork.

In this paragraph, I was not addressing the Prince Ernst August question, but only that of titles being given by the Queen to those within the Royal Family. Any cites to the effect that HM had to consult the PM prior to making Andrew Duke of York, for instance, or William Duke of Cambridge, on their wedding days?