Hi,
There's not a lot of information available on the DP pistols, however it's my opinion the DP most likely stood for 'Demonstration Pistol'. This was also Clive Law's opinion the last time I talked to him about this subject (RIP Clive).
As most milsurp collectors already know, DP markings were often hand stamped at the Unit Armourer or Base Workshop level for Canadian weapons deemed as 'Drill Purpose' only, meaning they were too worn or damaged to be used as anything but practicing drills, and not to be issued for operations or firing. If you don't already know this, you should keep it in mind next time you see a hand applied 'DP' marking on a rifle you're considering, as at some point it was deemed by the military too unsafe to fire.
However, something is different about the rare 'DP' series Inglis pistols.
The very few known genuine DP marked pistols had the markings factory engraved on the slide, frame, and barrel at the time of production. Of the observed DP pistols and the original example I owned these were near mint guns, mine was likely never even fired and belonged to an engineer at the plant. It was sourced threw the engineers family who had contacted Clive Law and he forwarded them to me. These original DP markings were not hand stamped on worn out old beaters, but factory applied to mint guns.
Another thing I was lucky to acquire was the factory shipping records of where most of the original DP series pistols were sent, and most of them were sent directly from the factory to foreign governments for testing. That's why I think the original DP pistols were meant as demonstration pistols.
For more information on genuine DP series Inglis's please check pages 110-116 of Clive Law's book 'Inglis Diamond' which is absolutely worth buying if you have any interest in these pistols.
You can also visit my website, I have some rare original Inglis examples photographed here:
https://www.combat-relics.com/inglis
I just took a look at the Switzers example for you and there are a few things worth considering. First that Switzers does not specialize in milsurps or militaria in general, they auction everything from guns, snowmobiles, farm equipment, hunting supplies, etc. and it's not surprising that many of their items are inaccurately described, and poorly photographed by collector standards. Watching their auctions I have seen many obvious fakes sell for ridiculous money, and also rare items sell for next to nothing. I guess that's why it's important you know exactly what you're looking at before bidding, and NEVER trust auction descriptions. Hit the books long and hard before throwing down your money, there's plenty of dealers out there hoping you will just rely on whatever they're feeding you, even the most reputable ones make mistakes.
The gun itself you're looking at is not like any original DP series Inglis. Like I already stated the originals are factory engraved on the slide, frame, and barrel. What this gun appears to be is one of the so-called 'Lunch Box' Inglis's (These are completely unmarked guns) that someone has attempted to incorrectly hand stamp a serial number onto. It's not the first time I've seen this done, there's a lot of fake Inglis's out there. A small note on the 'Lunch Box' guns, I believe many of the all black unmarked guns were sold surplus at the end of the war, and not true 'Lunch Box' guns which would have been stolen from factory in some guys lunch box maybe several parts at a time. Very few true 'Lunch Box' guns exist, and the ones that do are never fully finished and usually in the white, but it's a cool story that has been used to sell the all black unmarked surplus guns which come around fairly often.
Back to the Switzers gun, there are a few possible reasons someone would apply a hand stamped DP serial number onto it;
It could be someone exported an original DP series Inglis out of the country (illegally) to get more money from it in the United States, and replaced it with unregistered 'Lunch Box' gun they applied the fake serial number onto so that they could 'replace' it in the Canadian restricted gun registry. Or perhaps they simply lost the original pistol somewhere, and needed a replacement to avoid the awkward situation of reporting a loss. Now they are possibly selling the replacement at auction to completely wash their hands of the situation.
Another possibility is that someone surfaced an unregistered 'Lunch Box' gun and decided to give it a serial number so it could be easily registered, probably done when you could register a restricted fairly easily over the phone.
Or perhaps someone surfaced an unregistered 'Lunch Box' gun and gave it a DP serial number so it would be more valuable, and registered it as such.
Regardless of exactly why someone hand applied a DP serial number onto the gun, it's one that should definitely be avoided. I wouldn't want to own that gun based on the fact it's a pretty obvious fake, and also because it's possible associated with illegal activity. A general rule of thumb is to just never buy any Inglis with hand stamped serial number, with the exception of those that have received the serial number from the RCMP for registration purposes.
Regards,
-Steve