In general for British bios I highly recommend anything -- yes, anything -- by Antonia Fraser. She's actually Lady Fraser (and a Nobel Laureate, which I didn't know until just now, thank you, Google). Her bio of Charles II is terrific as is her The Wives of Henry VIII. If you want a dramatized bio, the recent Wolf Hall (about Thomas Cromwell) is an interesting read. Quite a different style -- written in the present tense, for one thing, which normally drives me batty but in this case it worked.