The tendency of the RN to treat its battlecruisers as battleships to give it 15 capital ships was understandable in these circumstances.
The inter-war Naval Treaties did not draw a distinction between battleships and battlecruisers. They referred to "capital ships". The 1922 Washington Treaty named the capital ships each nation could retain. For Britain that included 4 battlecruisers - Tiger, Renown, Repulse and Hood. Under the 1930 London Treaty Tiger, along with 3 of the Iron Dukes were to be scrapped with the fourth, Iron Duke, converted to a training ship. The ships on the lists were each navy's most modern at the time.