Hi and welcome to the forum.
The other 2 marks are the crowned leopard's head mark for London and the date letter which I think is probably P for 1770/71. WC is probably William Collings. The words are Latin; I can read the top word, fortiter, which means bravely, but I'm not sure of the other two. The whole is the motto of the family whose armorial is the dog below the motto and they would have been the original owners of the spoon. If you can read the other 2 words it may be possible to give the family name.