Hello,
As Silverport has said the makers' mark isn't the one registered by Yapp & Woodward not least because the mark they registered had a rectangular outline.
The item wasn't assayed in 1846. If it had been it would carry a Duty Mark showing Queen Victoria's head in an oval shape.
As Silverport has also pointed out there are anomolies with the marks shown. He has said Norton & White didn't register a mark at Bimingham until 1900 and it would normally be expected that all their assayed work was from that year and not before. There is however some evidence at
http://www.silvermakersmarks.co.uk that they were actually submitting work for assay from 1894.
There is also an anomoly with the outline shape of the date letter which would be expected in an oval outline, the letter style being lower case Gothic which the Assay Office only employed for one sequence, the letter "t" being for 1893-4. There is evidence however at the Birmingham Assay Office website
http://www.theassayoffice.co.uk/date-letters in the introductory paragraph that "there may be some variations in background during the late 19th century---".
With this additional information attribution to Norton & White as makers and an assay of 1893-4 is more certain.
Mike