You only have one of these
Most papers in this trade can be reordered in a week. This one cannot. Anyone reading up on how to legalize a Certificate of Naturalization is holding a document that came at the end of a long application, and replacing it means going back to the department that issued it and waiting again.
So the first decision is what actually travels. A notary makes a certified copy, that copy carries the notary's signature, and the chain runs on the copy from there. The certificate you were given stays at home, which turns a lost envelope from a disaster into an irritation.
The three stages
Consular legalization of a Certificate of Naturalization in the United Kingdom follows the same order as any other paper: a notary or solicitor first, then the FCDO, then the mission of the country that will read it. The FCDO stage costs around £45 and is run entirely by post out of a Milton Keynes box number.
The embassy legalization of a Certificate of Naturalization in Leicester is therefore finished overseas rather than here. Each mission sets its own fee, which is why no single figure covers this job, and each keeps its own diary, which is why the British turnaround is only part of the wait.
What the far end is checking
The office abroad is usually after two things: that the certificate is real, and the date citizenship was granted. The stamps answer the first. The second is already printed on the paper, which is why a partial copy or a photograph of one side gets rejected while a full certified copy passes.
That is also why to legalize a Certificate of Naturalization in Leicester you should copy every side of the document, including any reverse that carries a reference. Notaries do this as a matter of habit, but confirm the copy is complete before it is bound, because unpicking a notarial binding means paying for the stage twice.
Timing, and doing it once
People rarely need this paper alone. A residence file usually wants a birth entry and often a marriage entry beside it, and those can be ordered fresh from Leicester Registration Service on Charles Street while the naturalisation copy is being made.
Running the whole set through together is the saving worth having. The embassy attestation of a Certificate of Naturalization in Leicester takes the same courier trip as the rest of the bundle, so one journey and one wait covers papers that would otherwise cost three of each.