The Begining just starts out with Alvin Lee playing the intro which goes like this.

e|---------------------------------------------------------------------------|
B|---------------------------------------------------------------------------|
G|---------------------------------------------------------------------------|
D|6-7-(b9)/11---6-7-(b9)7-6---4-6-7-6-4---2-4-0-2--------------------------------|
A|---------------------------------------------------------------------------|
E|0-0-0--0----0-0-0-0-0---0-0-0-0-0---0-0-0-0--------------------------------|

The Bass comes in on the second time around and Leo Lyons just hits the notes which are:

G|---------------------------------------------------------------------------|
D|---------------------------------------------------------------------------|
A|/7------/7-(b9)5-7-------------------------------------------------------|
E|---------------------------------------------------------------------------|


Right Before the Chorus Alvin stays on an E chord for 4 measures.

Then for the chorus it goes:


e|5--5--5--5---3--3--3--3---0--0--0-------------------------------------|
B|5--5--5--5---3--3--3--3---0--0--0-------------------------------------|
G|6--6--6--6---4--4--4--4---1--1--1-------------------------------------|
D|7--7--7--7---5--5--5--5---2--2--2---2p0-------------------------------|
A|7--7--7--7---5--5--5--5---2--2--2-------2p0---------------------------|
E|5--5--5--5---3--3--3--3---0--0--0-----------3b0-----------------------|

Right after the Chorus Alvin goes back and fourth with chick churchill the keyboardist 
the parts go something like this:


e|---------------------------------------------------------------------------|
B|---------------------------------------------------------------------------|
G|(b9)7-6-4-2----9p8-(b9)7p6-7-6p4-6-4-2-1-1-------------------------------------|
D|---------------------------------------------------------------------------|
A|---------------------------------------------------------------------------|
E|0-0-0-0-0------------------------------------------------------------------|

So it does that for maybe 3 or 4 times then back to the E chord for 8 measures this time 
the coolest part in the song:

e|0-0-0-0---2-2-2-2----0-0-0-0------------------------------------|
B|0-0-0-0---3-3-3-3----2-2-2-2------------------------------------|
G|1-1-1-1---2-2-2-2----2-2-2-2------------------------------------|
D|2-2-2-2---0-0-0-0----2-2-2-2------------------------------------|
A|2-2-2-2--------------0-0-0-0------------------------------------|
E|0-0-0-0---------------------------------------------------------|

Then it just repeats that and the solo comes in which is obviously in the key of E.
Also if I could recommend there is an amazing live version of this song on Ten Years 
Live At The Fillmore East its great.