Two signatures, two different claims
It helps to see these as separate promises. The translator promises that the Russian says what the English said. The notary promises nothing about the Russian at all — only that a particular person signed in front of them. Muddling the two is how people end up paying for a notarial act that the office reading the file never wanted in the first place.
What usually triggers the extra step
Notarisation tends to attach to documents that create obligations rather than record facts: powers of attorney, company resolutions, declarations made under oath. Plain civil records more often travel with the certification alone. The wording of the request you were handed is the best guide there is, and it is normally explicit whenever a notary is wanted.
The Russian itself
Whatever route the paperwork takes, the writing is the same job. Every field is rendered, including the ones people skim past: issuing office, reference numbers, marginal notes and anything added by hand. Seals and signatures are described where they sit rather than turned into sentences, so the Russian page can be laid beside the English one and matched mark for mark.
Rate, clock, and where the paper comes from
The rate is £25 for each side as issued, and the standard window is 2–4 business days from a clean scan, or 24–48 hours on express. Where the source is a birth, marriage or death entry, Derby Register Office at Riverside Chambers, Full Street, Derby DE1 3AF issues fresh certified copies, and a notarial act, where one is needed, carries its own official fee on top.