Wildthyme on Top (anthology)

 was a Big Finish novel released through their New Worlds imprint in 2005.

Publisher's summary
Iris is an enigma... She's an enigma wrapped in a mystery. With a shapeless, tasteless hat clamped to her head. She's an enigma wrapped in a mystery, with a shapeless, tasteless hat clamped her head and she's puffing on a gold-tipped black Sobranie. And she drives a big red double-decker bus, ostensibly bound for Putney Common. Except it's not. She's been to Putney Common precisely once and that was by accident. That was when she picked up Tom, who is now her best friend. Together they journey through the multiverse: boozing and fighting; righting wrongs and buggering things up again. Here, in their first exciting anthology of ludicrous adventures they meet monsters, killers, ambassadors, insect-things, detectives, weirdos, psychics, fiends and sundry perverts.