Newest non-Royal dukedom

In a quiz yesterday I was asked "Which is the newest non-royal dukedom
in the peerage in England (sic)?"

I said Fife, the answer wanted was Westminster. Any views on which (if
either) was right?

Al...

It's Fife. creation of 1900 in favour of Alexander Duff, 6th Earl Fife.

Don Aitken...

It depends on how you define your terms. Fife was not a dukedom of the
blood royal, but the grantee, being the Queen's grandson-in-law, was a
member of the royal family.

Even ignoring Fife the Dukedom of Argyll (1892) & Gordon (1876) were
before Westminster (1874)

Don Aitken...

True. If you want the answer "Westminster", the question should be
"Who was the last person outside the royal family to be made a duke?"
(Argyll and Gordon being dukes already).

Hovite...

But the original question said "in England", which rules out Fife,
Argyll, and Gordon.

Don Aitken...

In fact, it said "in the peerage of England", which means that the
correct answer is Rutland!

Hovite...

"in the peerage in England"

Hovite...

You were answering a different question. Westminster is "in England",
whereas Fife is not.