Hi I am learning Waterloo sunset by the Kinks in the original key of E now every tutorial and chord sheet show the first 3 chord progressions are E B A. I have just last week bought Justin’s vintage songbook and the chord progression is shown as E B7 A, to my untrained ear this does not seem right
try it and you will see what I mean which one is correct. B7 does not appear in the E key but B does.
John @Guitarman
I am perhaps stepping into deep water.
B chord is a triad, three notes whereas B7 has four notes, a flattened 7th is added. As far as I am aware you can use B7 instead of B, it is more a matter of taste or preference. B7 may be used for a particular reason such as secondary dominant but not sure I am the best person to explain.
Michael
Yes B7 is in the key of E. The B is the V chord of the key, and as such it’s 7th is flattened. It’s the only Dominant 7 chord in the key, the other major chords (the I and IV) form Major 7th chords.
B7 contains the b7 of B which is the note A which is certainly in the key of E.
I’ve seen versions of the song with a B7, however I do agree with you that a ‘regular’ B sounds nicer to my ears played on a solo guitar. I do suspect Justin is technically correct though 
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Out of curiosity, I watched a couple of videos of the Kinks (or Ray Davies) playing it live. Davies plays the acoustic guitar and you can clearly see that he plays B7 in the open position.
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As @mathsjunky correctly says, B7 is not a secondary dominant.
It is the true primary dominant in the key of E.
The chords in E major as triads then extended to 7ths.
E → Emaj7
F#m → F#m7
G# → G#m7
A → Amaj7
B → B7
C#m → C#m7
D# → D#m7b5
The V chord played as a regular major chord is the dominant and provides a perfect cadence, tension to resolution, when going back to the I tonic chord.
Even more so when the V is played as a V7.
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Richard @Richard_close2u
I said I was perhaps stepping into deep water, it was deeper than I thought!
Michael
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thanks for your comments B7 is easier to play than an A shape B, but B sounds nicer will learn both ways.