A bunch of titles to my personal taste from the Kindle UK monthly deal that expires tomorrow - sorry about the short notice, got busy and forgot about it. Also, I apologize if some of these have been mentioned up-thread - per "busy" above, I don't have time to search all of these, so just popping them out here.
At £0.99
Fool Me Once by Harlan Coben:
https://www.amazon.co.uk/Fool-Me-Onc...dp/B015PEXCGO/
Dust by Patricia Cornwell:
https://www.amazon.co.uk/Dust-Scarpe...dp/B00CQ5R18G/
Flesh and Blood by Patricia Cornwell:
https://www.amazon.co.uk/Flesh-Blood...dp/B00KA1035Q/
Smiley's People by John le Carré:
https://www.amazon.co.uk/Smileys-Peo...dp/B002V092EC/
The Honourable Schoolboy by John le Carré:
https://www.amazon.co.uk/Honourable-...dp/B002V092KG/
The Constant Gardener by John le Carré:
https://www.amazon.co.uk/Constant-Ga...dp/B002V091Q6/
The Mission Song by John Le Carré:
https://www.amazon.co.uk/Mission-Son...dp/B002V092SI/
A Quiet Flame by Philip Kerr:
https://www.amazon.co.uk/Quiet-Flame...dp/B0038QN2BM/
Bats in the Belfry: A London Mystery by E. C. R. Lorac:
https://www.amazon.co.uk/Bats-Belfry...dp/B078HWKW7W/
Blood on the Tracks: Railway Mysteries by Martin Edwards:
https://www.amazon.co.uk/Blood-Track...dp/B07BGCR7C7/
Whispers Under Ground by Ben Aaronovitch:
https://www.amazon.co.uk/Whispers-Un...dp/B007704UFC/
At £1.19
Dominion by C. J. Sansom:
https://www.amazon.co.uk/Dominion-C-...dp/B008PQ8UX0/
At £1.99
The Leopard by Jo Nesbo:
https://www.amazon.co.uk/Leopard-Har...dp/B004FV4XBC/
More later if I get time...