Mumford & Sons played "The Cave" in the key of E major. That is the key for both the Guitar and Banjo arrangements.

The banjo will have to be tuned DOWNWARD in pitch 1.5 steps to the key of E. This is the same exact interval configuration as the standard open G tuned banjo...except 1.5 steps lower. So all chords and scale patterns will be played identically to what they would be in the standard G tuning. If you're only reading the tab and not listening to the MIDI file... you could just play the song in G... 

The guitar version is what I set up first, to get everything in order for the banjo arrangement. The guitar version has no banjo in it other than the melody line where the lyrics are. The guitar version emulates what the guitar did in the Mumford & Sons recording... mostly playing arpeggios fingerstyle or with a pick... Key of E. Moderately Easy.

The Banjo version is on it's way... Not finished yet. The arrangement itself will be identical to the guitar version, except that I will have the banjo playing what was played by the guitar. Key of E also.

Both arrangements are Moderately Easy.

Lastly, I will send both Guitar AND Banjo arrangements for the same $2. Also included will be the Chord & Lyrics sheet in PDF form. A must for every Mumford & Sons fan. 

Tom