You're in luck; it appears to be the same medal as the one listed as number 1345 in the Eimer catalogue of British medals. It was issued in three metals: silver, bronze and "white metal", a kind of pewter. From my understanding of the catalogue description, the silver one was issued at 45mm diameter, the other two at 39mm. From the colour it obviously isn't the bronze one, but the size should tell the difference.
The silver one lists at £320 in EF; the pewter one at £70.
The ring-clasp and suspension loop were added at a later date; they may lower the value of the medal, especially if whoever added it damaged the medal in the process.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis