Lock, Stock and Two Smoking Fireballs / World of Donlon / London

Donlon → London

Donlon is a distorted version of London. And there are many references in names and places to the real London. 
Small disclaimer: I am not Midge, below is my interpretation 🙂

The city of London

Donlon → London
A phonetic reversal: Swap the syllables.

The Flow → The Thames 
The Thames flows through London's heart exactly as the Flow does through Donlon.

Hellsea → Chelsea
Chelsea is one of London's most expensive and exclusive neighbourhoods. 

Poxhall (Bridge) → Vauxhall (Bridge)
Vauxhall sits on the South Bank of London.

Sheepley → Cheapside
Cheapside is in central London. Near Southwark Bridge, where the London Sheep Drive takes place. 

Thorough Market → Borough Market 
Homophone. Borough Market is London's most famous food market. Also famous for overpriced chocolate covered strawberries. 

Songbird Docks → Canary Wharf
London's East End docks were its historic commercial heart
Canary Wharf sits where the old docks once were. Canary, songbird. 🙂 

The Whitehall → Whitehall
A direct lift.
Whitehall is in Westminster where most of the UK government is based.

Bridge of Towers → Tower Bridge
Directly inverted. 

The Pit → Victorian underground fighting rings
London has a long history of (animal) fighting pits, in the East End and in Southwark. The Kray Twins started their careers as professional fighters. 

Slobberstalls Market → Spitalfields Market

Gangs

The Bigwhigs → The Bigwigs
'Bigwig' is British for a powerful or important person.
Derived from the large powdered wigs worn by the men in power in the 18th century.

The Mudlarks → Thames Mudlarks
Mudlarks were real.
In Victorian London, poor children and adults scavenged the Thames mud for anything of value they could sell.

The Mobgoblins → East End gangs
A mix of 'mob' (organised crime) and 'hobgoblin.'
In London in the late 1800s, there were many gangs in the East End. Like the Kray brothers. 

The Queenly Court of the Carnabal → The Royal Court / Notting Hill Carnival
The West End is London's theatre and performing arts district. One of the theatres is named the Royal Court. 
'Carnabal' is the Spanish word for 'Carnival'.
Each year in Notting Hill, there is the Notting Hill Carnival (in West London), Europe's largest street festival. 

Street Genies → London street art / Banksy culture
Street art and graffiti can be found throughout London. With Banksy as the most famous artist. 

Characters & names

The Krag Twins — Phil and Grant → The Kray Twins + the Mitchell Brothers (EastEnders)
'Krag' probably comes from Ronnie & Reggie Kray, mobsters and professional fighters from the 1960s. Known for violence.
'Phil and Grant' comes from the Mitchell brothers from the British tv show EastEnders. They are basically thugs. Fiery tempers and a tendency to resort to violence.

Percy Greenwood Tips
P.G. Tips is a famous British tea brand by Lipton Teas

Magpie
A bird known for collecting shiny objects. 
In British folklore, a single magpie is a sign of bad luck.

The Queenly Court & Mercury → Freddie Mercury / Queen
Sam joked about it and probably true. 
The Queenly Court → The band Queen.
The Mercury → Freddie Mercury was the lead singer of Queen. Known for theatrical performances.

Silt Saint Vulpin → Thames silt + vulpine
'Silt' is what covers the Thames river banks. Mudlarks went through the silt to look for valuables. 
'Vulpin' comes from 'vulpine', fox-like

Other things

Cathlon → Canton (Guangzhou) / Ceylon (Sri Lanka)
The Black Tea in the story comes from Cathlon, which could be a reference to Canton (modern Guangzhou) and Ceylon (Sri Lanka). 
Two places the British Empire got their tea from. 
Cathlon is described as a far-off and mysterious land working 'dark miracles' with their products. 

Redwush/Redwoosh→ Rooibos ('red bush') tea
Sam calls the tea Pete is given to drink 'Redwush/Redwoosh', most likely this is 'red bush' or 'rooibos'. A herbal tea from South Africa.
Rooibos is naturally caffeine-free. It is the lowest type of Tea in Donlon. 

Cillite Bombarda - Cillit Bang
Cillit Bang is a British cleaning product whose advertising slogan is 'Bang! And the dirt is gone.'
Saint Bartholomew Scott is Barry Scott, the Cillit Bang spokesman. 

Esme's Club → East End music halls and nightclubs
The Kray Brothers ran several nightclubs as social fronts.

Kintsugi / Porcelain → Japanese art -Victorian chinoiserie
Pete repairs the cracks in his porcelain by melting gold coins with his steam and putting pieces back together. 
Kintsugi, repairing broken pottery with gold. arrived in Britain in the Victorian era. When they developed a love for Japanese art
In the same era, the British also imported porcelain from China. That´s why it´s also called china. 

Carlos → Connections with Spain
Carlos has a Spanish name, speaks Ancient Ratin (Spanish), and had a girlfriend with a Spanish name. 
This is not out of place in Victorian London. In the 18th and 19th century.
Merchants, artists, refugees came from Spain to London and had a close-knit community in West London.