Barry Letts took over as producer from Derrick Sherwin after "Spearhead from Space".

Entity and relation annotations:
id: 0
type: entity
value: text: Barry Letts
labels: <Person>
id: 1
type: entity
value: text: "Spearhead from Space"
labels: <Work_of_art>
id: 2
type: entity
value: text: Derrick Sherwin
labels: <Person>
id: 3
type: entity
value: text: producer
labels: <Title>
type: relation
to_id: 1
labels: Person:creates:Work_of_art
from_id: 0
type: relation
to_id: 3
labels: Person:holds_title:Title
from_id: 0