Think zookeperz has now covered much of what I have just typed, but here goes anyway!
I believe this is a Gouby Date Style A
http://www.michael-coins.co.uk/cp_1858.htm
Pictures of one of my own examples attached; think exact same dies, noting the following:-
· Same die flaw to front of truncation, looks to be a bit more developed on your piece
· Same die flaw as your piece (highlighted with red arrows) around the T of VICTORIA
· Not pictured, but my example also has an additional obverse flaw running through the base of the TIA of GRATIA, same as on your own coin
· Same very close REG colon position, note G repaired
· Same N’s of BRITANNIAR, particularly noting the clumsy 2nd N repair
· Date has small additional piece to inner bottom loop of the 1st numeral 8 (again highlighted with arrow)
· 8’s seem a little ‘pointed’ at top left of top loop (again highlighted), yours may have an additional mark which I think has suggested to Pete it may be an overdate……...which I don’t think it will be!
Not a particularly rare variety in my opinion, colons on the Victorian copper penny series are all over the place!