It is a rather battered commemorative issued by Sevenoaks for Queen Victoria's golden jubilee. It is in white metal (soft pewter) which is why it is so easily knocked and damaged.
It is listed as 2451F in Andrew WHITTLESTONE Michael EWING's Royal Commemorative Medals 1837 - 1977 Volume 2. Queen Victoria's Golden Jubilee 1887. Second Edition, Galata, 2013.
In the condition it is in I would class it as a space filler only.