No point in that as all U.K. phones sold in the U.K. from December 2021 are not allowed to be locked to a carrier network, (Commonly referred to as, "Carrier locked") and will only operate on a specific carrier's network and require unlocking from it. See...
This, however, does not affect, "carrier branded", phones that are unlocked but run a carrier's own firmware. Put simply, whilst the phone will be carrier unlocked, (most, if not all phones in the U.K. already are), they can still run a carrier's own version of the manufacturers stock firmware with splash screens and their own apps and settings.
To check if your phone is running, "carrier branded", firmware, apart from seeing splash screens, apps or settings, Samsung use CSC codes, (Country/Carrier Software Code), that dictates the firmware version each device receives. To locate and understand your CSC code, see post #3 of this thread...
Hope that helps! 😁
Your phone is unlocked to run on any network, most U.K. phones already are. However, it will only receive O2 carrier certified firmware which is usually slower than stock Samsung firmware and is not eligible for Beta testing.
Buy from non-carrier retailers such as Samsung, Argos, Carphonewharehouse, Amazon and eBay, (usually check for the last 2), as well as numerous other retailers in the U.K.
I have not purchased a phone through a carrier since the Galaxy S2 and always purchase outright from Samsung directly.
However, as my girlfriend did, you can get non-carrier branded phones on contract via places such as Carphonewarehouse. Always check with the seller that they are providing a non-carrier branded device and not simply a carrier unlocked model.
My current device was purchased directly from Samsung, however I have had contract phones in the past. Whilst buying outright will not be suitable for everyone it is possible to obtain a non carrier branded device from other sellers as @ironass explains. However personally generally I would not be keen on using ebay for electronic devices when there are other options.