Sorry to be tardy. I'm guessing that there is no spread eagle with shield and an e pluribus unum banner, or you would have mentioned it (or the etching is just that worn).
British manufacture typically for the US market in the 1820s/1830s. Likely (most likely) says Warranted at the base of the blade. Is there anything on the spine at the base? The blade seems original to the blade but the grip may have been replaced (even back then) and carved in the current stylings. That seems just a little coarse for the type of work but then again, maybe not.
I would not start right off with scrubbies but give Evapo-Rust a try. Either create a pvc tube or just dampen/soak a towel and wrap the blade. Or, just repeated brushing. Check after soaking for an hour or so, don't just let it go overnight and follow the directions but on the side of caution. If left too long, a blade will get a deep gray etch.The rust doesn't look that bad and I even see some bluing remaining.
I use a variety of less abrasive polishes. I like Noxon and Nevr-Dull but also have some Flitz and Simichrome. Even without the Evapo-Rust, I have used Noxon. Noxon has some Oxalic acid and if you shake well, lather on and let it set until dry, you can rub off a lot of grime and surface rust. The bluing will literally disappear in solvents and major abrasives.
Without old journals linking the sword to one of the ancestors, the provenance is anyone's guess. A nice sword for display. The guard could be carefully straightened with some heat and a jig in a vise or other techniques.
Something similar imported by a fellow in New York City. He went to England in his teens to apprentice and then came back beginning an import and hardware business in the mid 1820s. His sword (and gun) imports lasted into the 1850s. This sword below would not have been marked so before the 1826 era.
Many blades were used up in England over a period of decades and sometimes you'll come across swords you might swear they were closer to 1800 until seeing the tell tale retailer marks or other defining characteristics.
Another Spies that could pass for the Napoleonic years. Imo, sold in the 1830s. Old surplus blades with some of the latest bling.
I think you do have a treasure there worth hanging onto.
Cheers
GC