"Royal" or "King's Own" title to British units

[Helios88]

This is not a topic about ranks insignia, and therefore I apologize if the thread is deemed being off-topic, but I have a deep-seated curiosity: how (and what are the criteria) a British military unit is awarded with the titles "Royal" (e.g. "Royal Scotland Regiment") or "King's Own"?

[60bill]

It's usually given for long and distinguished service or for an act of gallantry by part of the regiment.
An example would be the regiments that received the honour for their service during the First World war.

[Necrothesp]

Also note that when a regiment or corps amalgamates or splits then a royal title is usually retained. For instance, the Royal Logistic Corps was created with the royal title as three of its constituents had it. And the Royal Corps of Signals and REME were almost immediately granted the royal title as they were split from corps that already had the title. This doesn't always pertain through: the Adjutant General's Corps didn't get the royal title although three of its constituents (the Royal Military Police, Royal Army Pay Corps and Royal Army Educational Corps) had it, and neither did The Rifles, although one of its constituents was the Royal Green Jackets.