I love
Zara,
Alice, and
Emilia, though I wouldn't consider
Emilia particularly British.
Isla and
Thea are okay but not my style. I hate
Harriet,
Imogen,
Freya,
Poppy,
Harper (since when is this British? It's in the US top 10),
Florence,
Phoebe,
Millie (as a given name),
Martha, Darcie,
Lottie, and
Scarlett and hope they don't cross the pond.