Below is a round-up of the birth announcements from British newspapers. Sources include a national paper (The Telegraph, The Times) and a broad range of local newspapers from across England, Wales, Scotland and Northern Ireland.
Sibling names are in brackets. No official surnames are included; any name ending in a surname is actually a middle name.
Boys:
Arthur Henry Rupert (Eliza Beatrice Mary)
Benjamin Peter
Bertram Philip Alexander
Christopher Alexander Hendrik
Flynn Oliver
Freddie Forrest
Frederick Oscar Peter (William)
George
George James
Jace Kasimir
Jack Wilfred Ernest (Rupert Henry Patrick)
Maximilian Alexander
Otis Theodore (Rupert & Rafferty)
Rupert Francis Henry
Wilfred Spencer Ives
Girls:
Astrid Jean
Lyra Celia
Maisie (Lewis)
Millicent Cosima Artemis
Octavia Annabel Philippa (Frank Lanoe Peter, Finetta Rose Elizabeth & Edward Pelham Henry)
Penelope Rose (Sebastian)
Reenie Joy -- named after great-grandmothers Irene and Joyce.
Sienna Felicia Brooks
Sophia Evelyn Lucy
Sylvie Imelda (Ludo & Ossian)
I cross-reference older BAs to find the full names of the siblings, however often they are missing (especially the eldest siblings, or for half-siblings) which explains why you will sometimes see something like: George Henry (Lucy, Emma & Jack Arthur). "Lucy" and "Emma" may well have middle names as well; I simply cannot find them online.
