Dog owners have been warned by police to be on their guard after an ice cream cone filled with a suspicious bright blue paste suspected to be poison was discovered on the lower slopes of Primrose Hill.

Royal Parks contractors were alerted to the ice cream cone approximately two weeks ago with police believing the substance could be Methomyl – an insecticide that is deadly to humans as well as animals.

The banned substance is thought to have killed three dogs at a Brent park earlier this year, with one dying after eating meat left on a grass verge that was “smeared in a blue paste”.

Police are not linking the blue paste poisonings in Brent to the case of five dogs who mysteriously fell ill after walking in Hampstead Heath last month.

Vets believe the Heath dogs could have consumed a recreational drug, but are still awaiting results from blood samples sent to the US for further analysis.

Police have urged anyone who sees a bright blue paste on anything in Regent’s Park or Primrose Hill to immediately ring 999 and stay clear of the item.