Crown and lion on a stud.
 

Any ideas which regiment these are from, and whats that little brass tang for.

Royal Marines, the tang stops the badge from spinning around by sticking in to the cap.

As Phil has said, Royal Marines, the lion & crown with the screw post is usually associated with officer's badges while the lion & crown with long pin is usually for a WO2.

Paddy

In 1978 I acquired from a RM unit stores at Ballykelly (and still have somewhere) a gold anod. with screw post and a gold anod. with long pin, it was explained to me by the NCO in the stores that that both were officers patterns, the screw post in the process of replacing the pin.
The ORs gold anod globe and wreath collar badge cost 40p I think it was, the officers cap badge / collar badge globe and wreath was identical other than that the globe was silver coloured, it cost £3.60, so officers wore the gold anod collar badge as a cap badge instead.