From pinterest.com/pin/197032552417882640/.
The Spencer was a short coat, just how short can be seen here. The tasseled draw string appears to be used for tying up the neckline in chilly weather. Each shoulder is decorated with a rosette.
Keywords: 1818, British, jacket, Spencer, high neckline, collar, long close upper puffed sleeves, rosettes, cuffs, ruching, tassels