Diane Sinnott has already catalogued 101 lots for the next of the thrice-yearly Mouseman sales at Tennants of Leyburn ahead of the June 19 auction, compared to an average of between 35 and 60 pieces.
Among the items accumulated over the past four months, most of which came from the estates of deceased collectors, are an English oak owl carving that is estimated to fetch up to £3,000 and a pair of triple mice bookends that could sell for £2,000.
A personal touch in the sale is the powder bowl and cover gifted to Patricia Kirk, from a well-known Kilburn farming family, for her 21st birthday in 1948. After her death in 2015, a relative inherited the bowl and only recently realised its potential value.
Diane believes that the durability and practicality of Mouseman furniture appeals to a range of buyers of all ages.
"There is growing interest in Yorkshire and worldwide, though most of the major collectors are still local. At the last sale, the carved owls simply flew in price. In 19 years of working here I've only had four other powder bowls, so they are very rare and fetch a lot of money. The last one sold for £5,200 and I've had owls go for £8,000 each before.
"English oak is indestructible and it cleans so well compared to mahogany. It is durable and it lasts a lifetime. When we sold the Leeds Girls' High School contents in 2008, there were buyers there aged from 18 to 80. It has commercial appeal and it has the best trademark too.
"It fits into every home, from flat to castle. Thompson was a draughtsman, so he understood practicality. A lot of people developed their affection for Mouseman because they went to school in Yorkshire or their local church had his furniture."
Although 'purist' collectors favour items pre-dating Robert Thompson s death in 1955, Diane says there is now a glut of later pieces coming up for sale that were bought by couples who married in the 1960s and 70s and whose children are now selling their estates.
"People don't always understand the significance of what they've inherited, but the popularity has just gone up so much in the last two years.
"I'll never get fed up of Mouseman! We are really lucky to still have the workshop in Kilburn and I would recommend the furniture to anyone - it is so useful."