I walk into a Southall shop with Sophie, an undercover agent, who asks an Asian man in his 20s behind the counter: "Can I have two white biscuits?"
He looks slightly alarmed but still walks a few feet to his left, lifts up a box containing chocolates and pulls out what looks like two 20 packs of Marlboro cigarettes.
Sophie then walks over the road to a different corner shop and makes the same request with success, meaning she has purchased four 20 packs of Marlboro cigarettes at around £5 each - close to £4.40 off the recommended retail price.
Why? Because they're believed to be counterfeit and suspected to have been smuggled into the UK illegally, costing the UK millions in lost tax and potentially exposing smokers to lethal ingredients including rat poison that some of the cigarettes are laced with.
Sophie is one of three undercover agents, along with Robert and Rory (not their real names), who have been hired by Will O'Reilly, a former Scotland Yard detective chief inspector.
Since retiring from the force in 2009 after 32 years, he has set up his own consultancy firm, hired on this occasion by cigarette company Phillip Morris.
Their job is to collect intelligence on the illegal tobacco industry to then hand over to law enforcement.
"I want to raise awareness because in the police I saw criminal gangs smuggling cigarettes making profits," Mr O'Reilly says.
"The risks are small for cigarettes by comparison to hard drugs."
More shops found selling illegal tobacco
Mr O'Reilly says that just one container of cigarettes - containing around 10 million single cigarettes - smuggled in from abroad costs Her Majesty's Treasury around £1million.
On this occasion in Southall, Mr O'Reilly believes the cigarettes to be fake after recognising that the boxes all display the same serial numbers.
The cigarettes, he adds, are likely to have been made in factories outside the UK and could be laced with rat poison and other harmful chemicals, and have increased fire hazards.
No arrests or charges are made during the coup, but Mr O'Reilly said the intelligence passed on to law enforcement, including HMRC and Trading Standards, could result in a caution, fine and ban on selling alcohol to the shop owner.
Incorrect health warnings
We move on to another road within Ealing and Sophie, Robert and Rory walk into three different shops, on the same road, and bring back a series of illegal cigarettes to Mr O'Reilly.
This time they're not thought to be counterfeit but are illegal because they appear to have been smuggled in from abroad without tax - and do not comply with UK health warnings.
Among the cigarettes are Belarusian cigarettes, Marlboro cigarettes, Rothmans cigarettes and Winston cigarettes - all with foreign health warnings.
The Belarusian cigarettes, Mr O'Reilly says, are "specifically made for smuggling. They are not sold legally anywhere in the globe.
"These are smuggled in by the container load."
Using technology installed on his phone, Mr O'Reilly scans the cigarettes and can track the area where the cigarettes were made.
During the final swoop, Robert drives east of Ealing to pick up cigarettes from someone who was advertising them on the internet.
After an exchange on the quiet street corner, Robert returns with a 20 pack of L&M Black Label cigarettes.
Mr O'Reilly adds: "It is satisfying work. I see the final results with people being prosecuted."
