By Simon Jessop and Gwénaëlle Barzic

LONDON/PARIS (Reuters) - The biggest investor in French software firm Quadient is calling on the board to consider a potential private equity bid worth more than 350 million euros for part of the company, according to a letter seen by Reuters.

Teleios Capital Partners, which owns more than 15% of Quadient, was referring in the letter to a media report that has been confirmed to Reuters by two sources with direct knowledge of the matter, that Accel-KKR is seeking to buy the company's customer experience management business.

Following the report, which sent its shares higher, Quadient issued a statement on Tuesday saying it had no intention of selling the business.

Quadient declined to comment on the letter when contacted by Reuters on Wednesday. Accel-KKR was not immediately available to comment.

In its letter http://www.teleioscapital.com/documents/2020-11-25-Teleios-Letter-to-the-Board-of-Quadient.pdf, Teleios said it was "seriously concerned" that such an offer "which we believe could create substantial value for all shareholders" would not be given a fair hearing by the board.

"We are making our views public to help ensure that all shareholders appreciate what is at stake, and that the Board fulfils its fiduciary duty to act in the best interests of the Group and its shareholders," the letter said.

Teleios said the company's current strategy was "misguided", citing recent decisions including a restructuring of the company, a move to cut the dividend and to embark on a large M&A progamme.

"We strongly believe that engaging... is in the best interest of all stakeholders... and that it is the Board's fiduciary duty to seriously consider the Offer and to do so independently from management," the letter said.

Teleios added it would "exercise all rights available" to hold the board accountable should it fail to act, and called for it to update shareholders by Nov. 30.

Shares in Quadient are up nearly 25% since the report of the approach.

(Additional reporting by Pamela Barbaglia;Editing by Elaine Hardcastle)