The Peter Grant books always reminded me a bit of the Matthew Swift books by Kate Griffin (one of the pseudonyms of Catherine Webb). The Magical London part anyway. She's in her Claire North phase right now (The First Fifteen Lives of Harry August), but I've always hoped she'd circle back to Matthew Swift for a bit of a reprise.
There's a different Kate Griffin out there who writes "Kitty Peck" books. They're part of a historical London Crime series that's pretty good in its own right--but that's a different discussion. Just know that all Kate Griffins are not Catherine Webb.
Richard Kadrey and his Sandman Slim books had the same vibe for me as well (though not London-based). I only read the first few, though. So I have no idea what direction they may have gone.