Duplex burner with an art glass base

I found this beautiful oil lamp in an antiques shop in Ft. Collins, CO. It was marked "very old" on the tag (?). The blown glass base is 5.5" tall, and wide. The blown art glass is iridescent, and when held up to the light, has a deep blue glow. The base has no markings of artist name, but you can see the pontil/punt mark from being blown freehand. The Duplex burner is about 2.5" tall with "Duplex Made in England" on both knobs. The clear glass lamp top may be a replacement, it's 10" tall.

Any information you can provide on this little gem would be very much appreciated!

Thank you,
Julie