I am going to stick my neck out here, hope I'm right.
If there is a Hannah Walton connected with the Arts and Crafts movement in Scotland she is so little known that her work could not possibly be "quite valuable".
Added later: Well I was wrong - see Anne's post below!!
There was a George Walton (1867 - 1933) who was retained by James Couper & Sons as their principal designer from about 1896 (after Christopher Dresser who designed glass for Couper's until the mid 1890s). Walton was an architect-designer in Glasgow, and his designs are described as similar to Christopher Dresser's Clutha glass, but more symmetrical, less extravagant, and with more aventurine and lustre patches. Perhaps the auction house expert got confused.
However, HW is not likely to be the signature of George Walton.
There was an H. S. Williams-Thomas who was a designer at Stevens and Williams, but didn't so far as I know use HW as a signature. There was a German glass artist called Hans Weber in the 1930s who used an H sitting in a W. And there was a Hugo Eduard Wolf who used block capitals H.W. in Bohemia in the 19th Century.
Having said all that, maybe you could show us a picture - I'm sure that would help.
Best regards
Angela (I am not Frank).
References:
Charles R. Hajdamach: British Glass 1800-1914, published 1991.
Cyril Manley: Decorative Victorian Glass, published 1988.
Victor Arwas: Glass: Art nouveau to Art Deco, published 1987.
Hugh Wakefield: Nineteenth Century British Glass, published 1982 (2nd edition)
Widar Halen: Christopher Dresser, published 1990.
Anne Geffken Pullin: Glass Signatures, Trademarks and Trade Names, published 1986.
Carolus Hartmann: Glasmarken Lexikon, published 1999.
Ivo Haanstra: Glass Fact File A - Z, published 2001.