"I wake up with a big smile on my face at the moment," says spy novelist Mick Herron.
And no, it's not because he's hit the New York Times bestseller list (though surely that's to come) - just that earlier this year he finally quit his job as a sub-editor and now writes full-time.
"I'd commuted from Oxford to London where I worked as a sub-editor for years. I worked very long days, getting on a train a 6.30 am. I was very time poor for a long time," he says down the line from his publishers office in London.
Indeed the genesis of the acclaimed series occurred as Herron was standing on a tube platform in 2005 - the day of London bombings.
"That was one of the reasons I wanted to write books on a broader canvas," he says.
"I realised that day that you don't have to be an expert on geo-politics to write about huge events; you just have to be around when they happen, that offers a way in. I realised that everyone around me was taking part in world politics just by being on the streets of London."
That switch to a wider canvas is now paying off.
Herron's second Slow Horses book Dead Lions (2013) won the CWA Gold Dagger Award, and the next Real Tigers - my favourite so far - was even better. The TV rights to the Slow Horses series have been sold and a pilot script written.
Herron's long been a critic's darling but finally readers too are waking up to his talents.
Jackson Lamb the series' foul-mouthed anti-hero - even has his own Twitter handle @jacksonlambed.
"There's an old saying - "happiness writes white" - it doesn't leave marks on the page - whereas grief and despair go much deeper... that's where the humour comes from too..."
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is Herron's 11th novel and the fourth in the Slow Horses series - which has been called "the finest new crime series this millennium".
Last month it won the Ian Fleming Steel Dagger at the CWA awards making it the second CWA Dagger he has won for the Jackson Lamb series, along with four further short listings.
His next -
- is out in February - and is set in the aftermath of Brexit and sees the UK dealing with another string of terror attacks.
You finish one Slow Horses book and you devour them all. The prose is immaculate, the humour deft, the characters interesting and relatable.
This is no parody of the form however.
"I don't have a great deal of time for parody," he says.
"I'm attempting to write thrillers that would work if the jokes were taken out."
So, who are these Slow Horses? They're a rag-tag bunch of misfits who've been banished from Regent's House (Herron's fictional stand-in for MI5).
They're there for offences both personal and political their vices are many - addiction, bureaucratic faux pas, failed missions - but it's considered too risky to fire them outright so they're banished to Slough House where they spend their days pushing paper. All long to get back to Regent House and active duty.
"I started with a cast - and I knew they'd be fairly broken individuals. Because I'm writing thrillers and I wanted them to be involved in what was going on they had to be either spies or police officers. If you write about police officers you have to know what you're doing, but if you write about spies you can make it all up - so I went with that."
That freedom to improvise extends to Herron's spy lexicon - phrases like "C and C" - calm and collect - and a "cold body" - a decommissioned spy.
"Yes, they're both mine. Spy fiction gives you the leeway to create your own lingo. This is following in the path of le Carre of course who invented so many terms which we all still use. I feel completely legitimised in doing the same thing. People often ask me - "do I know spies or have I been approached to be one?" The answer is no - none that I know of. The Slow Horses are my creation."
Heading the team is Jackson Lamb - he's rude, slovenly and border-line alcoholic. He wanders through one book with cheese over his pants.
A typical day at the Slough House?
One Slow Horse skiving off work by practicing their waterboarding technique on a colleague, who promptly topples over and breaks a chair.
And here's Lamb greeting his rag-tag band of espionage misfits in the morning -
"... seeing you all together, it reminds me why I come to work every morning... It's because I've a cockroach infestation at home".
"Yes Lamb is offensive, but he's also very aware that he's offensive," says Herron.
"I've had experience of people who are offensive but don't realise they're being so, and that's a problem. But a character who is aware of what he's doing he's having fun and the reader can share in that fun - you enjoy it because he doesn't care."
Herron describes Lamb as looking like the English actor Timothy Spall gone to seed.
Herron's humour is tinder dry.
I'm not the first to suggest the Slow Horses books are a cross between the UK TV series The Office (set in Slough Herron points out, although he says he was only made aware of this later; the Slow Horses' run-down HQ Slough House is actually in Finsbury) and a John le Carre novel.
"I worked in an office for a long time and anybody who has understands the bitterness, humiliation and frustration of a career that's going nowhere.
"It's more fun to write failure than success. There's an old saying - "happiness writes white" - it doesn't leave marks on the page - whereas grief and despair go much deeper. And that's where the humour comes from too - the characters sniping at each other all the time. They wouldn't be doing that if they were happy. Having that kind of dejection in their stalled careers is what enables the humour to come through and allows the characters to come to life. If you're heroic all the time then all you have is action, whereas if you have introspection it allows insight into characters and emotions."
Despite his lassitude and challenged personal hygiene when Lamb's authority is challenged he's fearless; and no-one messes with his Slow Horses.
"Lamb has a moral code which he's very loyal to. He's old school - the active agent in the field is sacrosanct and he protects them. I think of it as - Lamb's shop floor but has been promoted to management but his heart remains on the shop floor. He doesn't like the people who're giving him orders and he doesn't particularly like the people he's giving orders to but if he's on anybody's side it's those on the shop floor."
I put it to him that fact is outpacing fiction and point to the bizarre death of Kim Jong-Un's half-brother in Malaysia at the hands it seems of North Korean agents.
"That just gives me licence to carry on and invent as outrageous plot as I feel inclined to," says Herron.
And are we all really Slow Horses to some extent - trying and failing on a daily basis?
"I think the best of us are," he says without hesitation.
"People who regard themselves as being successes are probably not looking very hard at themselves."
Spook Street the fourth Jackson Lamb novel is out now. London Rules is out February.