John Hubbard Antiques has dated this piece to the 19th Century.
Beautiful gold and embossed leather in black, with three "secret drawers" and a side drawer locked by a brass concealed internal lock. Original working key for inner compartment. Alas, no key for the main Bramah lock. As an interesting aside, there's a set of printing plates included for presumably a previous owner. See images for details.

Stock no: 4679
Circa 1830
Size: 19.5/8" wide x 10.1/2" deep (21" open) x 9.1/4" high
Dealers note: This is an exceptional, very large, writing slope in wonderful condition. Almost certainly the best currently available and without doubt the best I've seen in over 50 years. Very rare and very original and with a host of features including a concealed side drawer and three secret drawers and original inkwells, all help to make this a superb gift for someone very special or even the most discerning collector.
John Hubbard Antiques has dated this piece to the 19th Century.
You can view the stock and full dealer information on the John Hubbard Antiques Profile Page