As it says it looks like a post 1812 British officer’s shako but with the brass plate of a 1st Portuguese regiment added. Most likely the 1st Cacadores as the 1st Regiment of infantry did not have a light company after Beresfords’s 1810 regulations. It is strange that the officer’s name is not known and that he was not issued with a new, regulation, Portuguese army hat but had to modify, what was presumably his existing British shako? It is also interesting to note that by then the Portuguese had adopted a stove pipe design of shako. I guess life ‘in the field’ was never straight forward and this may be an example of improvisation!
Paul