For what purpose? If it's simply for performing in public, the copyright is dealt with through the licence fee paid to the rights management organisation, which in the UK is PRS. A performer doesn't have to worry about copyright.

If it's for a recording, then again it is usually handled by a rights organisation. In the UK this is MCPS. You submit a list of all the tracks and they work out a royalty fee for those which are copyright and give you a licence. The factory won't press the CD without this.

Digital releases are a bit different but there are licence arrangements for most situations.

Of course not all composers belong to PRS/MCPS and you may have to negotiate direct with the rights holder. In this case, since the song has been used in a film I would guess that the rights holder (who may not be the original composer) is probably a member.