Air refueling plan for Black Buck 1, 1 May 1982.
                                        Urban Fredriksson 1993 Jan 27

Aircraft Red 4 and Red 6 are the Vulcans.

-<- direction of fuel transfer
|   aircraft flies on
r   aircraft returns to base
*   the actual attack
Red and Blue are the outbound formations, the White is the
one meeting the Vulcan on the way back.

airborne
reserves                                                           airborne
   V              V                                                reserve
R5 R6     R2 R1   R4 R3                 B2 B1    B4 B3    B6 B5    B7
r  r      |-<r    |-<|                  |-<r     |-<r     |-<r     r
          |       |-<r                  |        |        |
          |       |------------<--------|        |        |
          |       |                     |---->---|        |
          |       |------------<--------|r       |---->---|
          |------------------------<-------------|r       |
          |       |--------------------<------------------|
          |       |--------------------<------------------|
          |---------------------------<-------------------|r
          |r-->---|
                  *
                  |---<---|r       |r
                  |       |-<r     |-<r
                  |       |  |     |  |
                  R4      W2 W1    W4 W3
                                   airborne
                                   reserves

In reality, it didn't turn out exactly like this.

The primary Vulcan developed a pressurisation fault and had to
turn back soon after take off.
Victor Red 2, which was to make the last refueling before the
attack broke off its probe and thus couldn't take on fuel. It
transferred its load to an other aircraft instead.
This aircraft turned out to have a fuel shortage on the way
back, but as radio silence was imposed it couldn't tell anyone
before the attack had been completed, and it was met by an
additional aircraft.
Same thing happened to the Vulcan, it was met by yet another
Victor that isn't shown either close to Ascension.

As the Vulcan pilots hadn't trained air refueling much, there
was a third pilot aboard, an instructor, to handle those.

So, we can see that the Vulcan only need one refueling each
way, but in case trouble developed, they wanted it topped up
as often as practical. (The distance from UK to targets in
USSR was much less than this.)