Traditional and British Standard night latches
Nightlatches are what most people refer to as a "Yale" lock. Most nightlatches will not be enough to validate your insurance company needs and generally should not be relied upon as your only way of securing the door.
It is possible to get nightlatches that conform to British Standard BS3621:2007 and in some cases are useful, although they are generally more expensive than a deadlock and so it is normally cheaper to have an additional deadlock fitted below the existing nightlatch.
Andy Stott Locksmiths can supply an ERA BS nightlatch at £75.00, the Yale equivalent retails from £118.25 and a BS deadlock is just £31.00. All three are kite marked and conform to BS3621:2007