The insurance specialist, which owns a total of nine brands, has asked the AAR to manage the pitch process. The incumbent on the business is MediaVest Manchester.
According to one source, BGL is expected to hold chemistry meetings with up to eight agencies before compiling a shortlist of four.
BGL's other brands include Budget, Dial Direct, the motorbike insurance specialist Bennetts and ibuyeco, the carbon-neutral insurance brand.
The decision to review follows a hike in investment in the comparethemarket.com brand and the recent appointment of Kal Samra as the managing director of the business. Samra, who previously ran Bennetts, is expected to oversee a budget of £65 million across comparethemarket's marketing and web initiatives.
In June, comparethemarket signed a £5 million deal with Channel 4 to sponsor its drama programmes.