I think someone has been pulling your leg, Nathan. Uniform is after all uniform and Queens Regulations, like US Army Regulations cover it.

Not all Peers and children of Peers in the British forces become officers.

I was in basic training with a Right Honourable James Golding (son of a Peer); was 'walking out' with a WRAF who was a Right Honourable Lady Jane (but was known as Bubbles); I was in-charge of training a SAC who was a Viscount (in his own right, not a curtsey title). None of them were accorded any exception to the uniform regulations.