Henry II UK Bronze Seal Medal - What This Is?

That's not Henry II of England - "Francorvm rex" is latin for King of France. That's Henry II of France, who reigned 1547-1559.

This medal probably isn't that old, either. Gilt copper medals were most popular in the 1700s and 1800s.

Being uniface (with nothing on the back) I suspect it may have been made as a decoration to attach to something else, rather than as a standalone medal; perhaps for inserting into a book cover or mounting onto a piece of furniture. It may be part of a series of medals depicting French kings throughout history, made for such a purpose.

I agree with Sap for two reasons:

The legend is: HENRICVS . 11 . GRATIA DEI . FRANCORVM . M . REX

That makes it Henri the second.

The other reason is that the image of Henri certainly resembles that of other coins and medals of this king. ( ref. 'Coinage in France from the dark ages to Napoleon' by Nicholas Mayhew pp 119 & 120, and Plate 24).

There is obvious gilding on this piece.

I'm having a small problem with the wording:
Gratia Dei as opposed to Dei Gratia, the latter being by far the more accepted usage.
The first translates as Thanks to God, the second as By the Grace of God
The mediaevalists will probably jump all over me, but I've never seen this conformation used in any documentation of the time, and I've read over seven thousand from France, England, Italy Spain and Germany.