Warwickshire Police has issued an appeal for witnesses after reports that a woman was sexually assaulted at Corley Services between junction 3 and 3a on the M6.
The incident happened at around 3pm on Friday 18 March.
A woman in her 20s had been in a coffee shop on the northbound side of the site and was walking towards Highfield Lane when she was approached by a man.
The man, who claimed to be a security guard at the site, accused the woman of removing items from the shop and told her she would need to come with him so he could perform a search.
The woman denied taking anything but the man then touched her inappropriately over her clothing.
When she told him she would call police, the man left the area in an unknown direction.
The man was described as white, between 20 to 25 years old, with curly ginger hair and a Scottish or Irish accent, and was wearing a black body warmer and blue jeans.
Officers are appealing for anyone who was on the northbound side of Corley Services between 2.45pm and 3.30pm to get in touch.
They are also urging people who saw the incident or who believe they can help with the investigation to come forward.
Anyone with information can call 101 or Crimestoppers anonymously on 0800 555111 quoting incident number 248 of 18 March.