Ratner plans to increase his bid for Signet's UK division, including the high street jewellery brands H Samuel and Ernest Jones from£200m to£350m, according to The Mail on Sunday.
In response, a Signet spokeswoman said: 'The company has not received any communication regarding a possible sale. Signet said in August that the UK arm is not up for sale.'
According to reports, Ratner said his bid was supported by an unnamed private backer and that Signet's largest shareholders were 'receptive' to his latest offer. Signet's shareholders include Harris Associates, which owns 13 per cent of the company, and Schroders, which owns about 9 per cent.
On Monday, The Telegraph aired speculation that Ratner might sell upmarket jeweller Ernest Jones if he succeeded in buying the two chains from Signet. A price tag of£175 million for Ernest Jones was suggested and Baugur, which owns Goldsmiths and Mappin & Webb, was singled out as a possible buyer, according to the report.