The Holland & Holland is a barrel-cocking bar action lock.
The Purdey is a spring-cocking bar action lock.
They work on entirely different principles.
The Holland lock is simpler, easier and cheaper to make and can cope with being made in lower qualities.
The Purdey lock is not easy to make, is costly to make and can only be made as abest quality gun out of the best materials. It is more complex and less conventional.
The Purdey lock was adapted by Atkin for production by his firm (also now made by Charles Hellis) and the Purdey lock will also be found on guns made by English gunmakers, notably Beesley, its inventor. David Sinnerton made a Purdey-action gun of superlative quality a few years ago and I have seen a decent copy by Ugartachea.
