Camden Council is seeking an Asbo against Horrox, managing director of Diabolical Liberties, which has previously described itself as a guerrilla marketing agency but now prefers the term "ambient media", banning him from authorising fly-posting anywhere in England and Wales.
The hearing against Horrox at Highbury Corner Magistrates' Court, North London, began last Tuesday and is set to finish by lunchtime tomorrow.
If the judge, James Henderson, grants the order, then Cardiff Council will formally ask for it to apply to the Welsh capital as well.
Other local authorities set to make similar applications are Lambeth, Westminster, Havering, Haringey, Ealing, Manchester, Salisbury, West Sussex, Gloucester, Newport, Exeter, Walsall, Tynedale and Bristol.
If the Asbo is granted, Horrox could face jail if he breaches the order.
Earlier Horrox's lawyer claimed Diabolical had carried out fly-posting on behalf of Camden Council for several years in the 1990s.
Camden Council's assistant director of environment (street cleansing) Alex Williams agreed, under cross-examination, that Camden Council employees might have commissioned Diabolical Liberties in 1999 to help publicise local events, but he said the authority would only deal with Horrox in future if he stuck to advertising on authorised sites.
Meanwhile, proceedings have been discontinued against Anna McAree, a staff member at Diabolical Liberties, and two former employees, James Heighway and Dominic Murphy, who have now founded their own firm, after all three undertook in court last week not to fly-post in Camden.
Heighway and Murphy issued a statement saying: "We're pleased that Camden has finally dropped proceedings against us. This episode has put us both under considerable strain and stress and we're glad to put it behind us. Both of us resigned from Diabolical Liberties early last year and have since set up Brotherhood Media, an independent media agency offering creative alternatives to fly-posting."
Earlier in proceedings, Cardiff 's street cleansing enforcement manager David Sandbrook said fly-posting had cost his authority up to 拢250,000 in clean-up operations in the past five years.
Sandbrook claimed Diabolical Liberties was linked to an operation called City Centre Posters, which was responsible for posters being regularly plastered illegally on residential and commercial properties.
Camden Council's Williams said fly-posting upset his borough's residents and damaged the local environment.
He said: "When the Hampstead and Highgate Express, for a stunt, fly-posted Diabolical Liberties' properties last summer, the employees were irritated by what had happened."
Horrox and his team do not concede that fly-posting constitutes anti-social behaviour under the act, which is defined as behaviour that is likely to cause "harassment, alarm or distress".
The hearing continues.