Embattled British pop star Tulisa Contostavlos has been dealt another blow after her best friend was warned by cops for allegedly sending a death threat to a tabloid reporter.

The singer was arrested on suspicion of supplying drugs on 4 June (13) after undercover journalists working for U.K. newspaper The Sun alleged she was caught on camera agreeing to arrange a cocaine deal in May (13).

Her pal and personal assistant Gareth Varey then allegedly sent a nasty email to the newspaper's investigator, prompting a police probe.

Police formally cautioned Varey after he admitted to the offense and he has since apologized.

The incident caps a bumpy week for Contostavlos - a man was arrested at her home in Hertfordshire, England, on Wednesday (12Jun13) on suspicion of harassing her after he turned up at the property in the middle of the night.