Horses have been found roaming Bannister Sports Ground, Oxhey Lane Farm and the Old Redding area leading officials to suspect the animals are being illegally traded.
Last week, 15 horses were found wandering on private land in the Old Redding area of Harrow, while eight more horses were caught grazing on playing fields at the Bannister Sports ground, in Uxbridge Road.
Officers from the Hatch End Safer Neighbourhood Team (SNT) and council officers are monitoring the Old Redding area of Harrow - a part of the borough with open farmland - to try and find the horses who have been trespassing and trace their owners.
Sergeant Pete Carruthers, of the Hatch End SNT, has been dealing with tracing the owners of the horses in the Old Redding area.
He said: "We are looking into putting up a notice and if we do not find the owners in 14 days they will be taken to a shelter.
"These horses have been there for around two weeks and we have got a lot of calls from residents, who have seen horses on the roads."
Householders have also reported cases of horses straying into gardens.
Seven horses have been found roaming in the privately-owned Oxhey Lane Farm and council officers are seeking to remove the horses under the Animals Act 1971.
Councillor Susan Hall, Harrow Council's portfolio holder for environment services, said: "On previous occasions we have worked closely with the police in seeking to put an end to an illegal trade that was causing misery to landowners and local householders alike.
"We will not hesitate to use the courts to halt a trade that flouts the concerns of local people and is a blight on the community."
On Saturday (January 24) a horse collapsed in a field in Old Redding and the RSPCA was called, however when they arrived the horse had been removed.
In 2007 Harrow Council won a two-year injunction against Nathan and Tina Jordan, of Oxhey Lane, Hertfordshire, who were running an illegal horse-trading business on private land in the Old Redding area of Harrow.
Up to 75 horses were involved in the business which was run on around 200 acres of land.
Harrow Council were awarded more than £18,000 in costs after a hearing at Watford County Court on October 3, 2007, and the couple were banned from setting foot on the land or encouraging others to do so, they both face prison if they breach the terms.