In which key are cadence of major chords: G D F C?

Question

I like a lot Pink Floyd's "Fat Old Sun" song from Atom Hearth Mother album. Its end is constructed around a quite usual cadence of major chords: "G, D, F, C". I wonder if this cadence is on the key of G (G is at the beginning), or in the key of C (C is at the end). If it is in the key of G, the F note of the F chord would be outside the G major scale, and if it is in the key of C, the note F# from the D chord would be outside the major scale of C. There is neither secondary dominants, so the situation is quite symmetrical.
¿Is there some general rule to resolve similar cases?

Answer 1

If you listen to the whole song, it's clearly based in the key of G. Note that the C chord that ends the final 'repeat to fade' loop always leads back to a G chord. Also note the D chord in my example is a pickup, the chorus progression actually starts with the G chord on 'fat'.

The bVII chord is so common in pop and rock as to hardly need a modulation or 'borrowing' to justify it.

No need to analyse the Am, Dm, Gm on 'The silver sound from a time so strange' earlier in the song as anything more than an attempt to be weird. This IS Pink Floyd after all! Weirdness was their thing.

Answer 2

I would say that the simple answer is that the song is based in G major but the F chord is 'borrowed' from G mixolydian.

I would expect to see the song written out in two sharps with naturals where the F chord is played.