There is (or was) a collection of Chinese Junk models at the Science Museum. It’s called the Wartz Collection. Wartz and Worcester were both officials in the Chinese Customs Service; apparently an organization from when British gunboats patrolled Chinese Rivers. In is book Worcester writes that he helped Wartz with the the collection.
Good catch! It was just a wild guess that there was a collection of Chinese models and Worcester was a British customs official on the Yangtse at the same time as the San Pablo was on the U.S. China Station, so... It looks like we may be getting closer to learning something more about this model. If it is as similar to the RMG's Chinese model collection as the OP said it was, it may have once been part of Wartz's collection, or perhaps built by the same modeler.
I did a bit of AI digging and came up with this:
Fate of the Science Museum’s Chinese Ship Models
The Science Museum in London once displayed a remarkable collection of Chinese junk models in its
Shipping Galleries, part of the Water Transport section. This display included the
Frederic Maze Collection of Chinese Junks, donated to the museum in the 1930s by Sir Frederick Maze, Inspector General of the Chinese Maritime Customs Service
hpchina.blogs.bristol.ac.uk. Maze was motivated by a desire to document what he saw as a “vanishing era” of Chinese shipping, and the models were intended to preserve the appearance and craftsmanship of these traditional vessels.
For over six decades, the Maze Collection was on public display alongside other global ship models, including British and foreign craft
hpchina.blogs.bristol.ac.uk. However, when the Shipping Galleries closed in 2012 to make way for the new
Information Age gallery, the models — along with the rest of the maritime collection — were moved to
off-site storage in specially constructed protective crates
Science Museum Blog. These crates buffered the fragile models from temperature and humidity changes that could cause damage.
The models remain in storage, with their protective covers left in place until someone requests to see them. In 2017, the museum invited photographers
Anderson & Low to document the collection through its protective casings, using ambient light to create painterly, atmospheric images. These photographs were exhibited in the
Voyages show, offering a new artistic perspective on the models while keeping them safely preserved
Creative Review+1.
In summary, the Chinese ship models from the Maze Collection are
still part of the Science Museum’s holdings, but they are no longer on public display. They are preserved in climate-controlled storage, occasionally brought out for special exhibitions, and have recently been showcased in a creative, non-traditional format to keep them visible to the public.
It may be that there were two Chinese ship model collections associated with the British Customs Service on the Yangtse, a "Maze Collection" and the "Wartz Collection," or, perhaps these two are actually one in the same, having maybe changed hands between private collectors and then been acquired by the Science Museum. It's also possible that these Science Museum models are those now in the RMG's collection. As I recall, the Science Museum deaccessioned a lot of their ship models with the lion's share being transferred to the NMG and the remainder being auctioned off by a London gallery in fairly recent times.
Anyway, perhaps this bit of information will motivate the model's present owner to investigate further with the curatorial staff at the Science Museum. I hope he does and keeps us informed of what he learns!