Why the Royal Navy did not need a pocket battleship

Should the Royal Navy have built its own pocket battleships?

No. Britain could build real capital ships and heavy cruisers, so the treaty-driven German compromise did not fill a useful gap.

Germany used the Deutschland design because treaty restrictions prevented a conventional capital ship. Britain could build full-size capital ships and was already considering powerful heavy cruisers, so copying the German compromise offered little additional value. An 11-inch battery would not create a decisive British advantage over a fast-firing 9.2-inch cruiser. The useful lesson is that the Panzerschiff answered a specifically German legal and force-structure problem rather than defining a generally desirable warship type.