In addition to the registration of a marriage or a birth, you can apply for a translation of certain documents (birth certificate, Driving license, Identity card) and a power of attorney (procuration).
No, you should make an application at the Consulate in London for the transfer of your registration file from the Embassy/Consulate where you were registered.
No, the expired document must be collected by the Consulate. In case of transfer of the leave to remain endorsement on the new passport, the expired one can be exceptionally handed over and returned back after completion of the procedure.