The building was erected in 1924, a design of Sir Reginald Blomfield. One of his better buildings, I think - I'm not great fan of his work - it is compact and well detailed, influenced by English Baroque and early French Neo-classicism. From Arts and Crafts beginning Blomfield went on to design in the Grand Manner on a large scale, of which the Usher Gallery is a well-mannered example. (I do love Victorian and Edwardian architecture, but I often find the overblown scale of some it, for instance in the work of Sir Richard Norman Shaw, really off-putting. It's just too overpowering.) Blomfield in his later career produced some really monstrous buildings like the Quadrant, Regent St (albeit he did have to incorporate the rear facade of Shaw's elephantine Piccadilly Hotel) and the Headrow Leeds. And there are his proposals for Carlton House Terrace overlooking the Mall, in London. Thankfully the Nash Terraces survive...
The odd thing is that architects like Blomfield, a Classicist, could be such a vandal, while early-Modernists like J M Richards such committed conservationists. Another blot on Blomfield's copy-book is his partial responsibility for the (British) electricity pylon! (Look closely at one; it's actually an obelisk...)
That said The Usher Gallery is a rather fine building. And he didn't like English Neo-Palladianism. So he got some things right.
I forgot to mention that Blomfield was a prolific writer on architecture, producing a number of histories on English and French architecture. He is perhaps, however, best remembered for his seminal book 'The Formal Garden' with its ravishing pen and ink illustrations by Francis Inigo Thomas. I like them almost as much as I like the work of FL Griggs. Thomas was no mean garden designer himself; he was designer of the exquisite Arts and Crafts gardens at Athelhampton.