This is Lance Corporal Sarjvit Singh of The Army Air Corps and Signaller Simranjit Singh of the Royal Signals. The two men are the first Sikh soldiers to wear their turbans while on public duties in London, which include guarding Britain's Queen Elizabeth II, and protecting the crown jewels in the tower of London: Sikh soldiers guard Queen Elizabeth II.
Ceremonial guard duties are normally carried out by Guards of the Household Division in their distinctive scarlet tunics and bearskin caps, but when the Guards units are busy with operational duties, other regiments step in. Thus, we have Sarjvit and Simranjit here, rocking their turbans and standing guard.