British fertiliser not starting transmission speed (3,4)

I believe the answer is:

bit rate

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'transmission speed' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'british fertiliser not starting' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'fertiliser' becomes 'nitrate' (I've seen this before).
'not starting' means to remove the first letter.
'nitrate' with its first letter removed is 'itrate'.
'b'+'itrate'='BIT-RATE'

Can you help me to learn more?

(Another definition for bit rate that I've seen is " Speed of data flow".)

I've seen this clue in The Daily Express.

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