What scale were the Avro 707s compared to the Vulcan?

When Avro set out to design the Type 698 bomber, the company had no experience flying delta wings. To reduce risk, it planned two smaller experimental aircraft based on the 698: the Type 707, at one-third scale, to study low-speed behaviour, and the Type 710, at half scale, for high-speed flight. Two examples of each were ordered. The French Wikipedia likewise describes the 707 as a single-jet 1/3-scale demonstrator.

The Avro 710 was cancelled because its development was judged to take too long. In its place, a fast variant of the 707 itself was designed, the 707A. The first 707, VX784, flew in September 1949 and crashed that same month; the second, low-speed aircraft, VX790, was built with the nose section of the 707A, redesignated 707B, and flew in September 1950, piloted by Roly Falk. The high-speed 707A, WD280, followed in July 1951.

Because of the programme's delay, the contribution of the 707B and 707A to the basic design of the 698 was not considered significant, although they did point to some necessary changes. What they did do was demonstrate the validity of the design and build confidence in the delta planform. A second 707A, WZ736, and a two-seat 707C, WZ744, were built afterwards, but they no longer played any part in the Vulcan's development. At the 1953 Farnborough air show, the two Vulcan prototypes flew together with four Avro 707s.

The aircraft originated from Air Ministry specification B.35/46.