Activist investor PrimeStone Capital has called on the board of Intertek to enter discussions with private equity group EQT following the rejection of the latter’s revised takeover proposal, according to a report by Reuters.

In a letter released on Monday, PrimeStone, which said it holds an economic interest of around 0.5% in Intertek through funds it advises, urged the company to engage more openly with EQT and grant access to supervised due diligence.

The investor also questioned Intertek’s valuation stance after the company dismissed EQT’s latest offer, which valued the testing and assurance group at approximately GBP8.9 billion, or GBP59.10 per share.

PrimeStone argued that the proposal did not materially undervalue the business and suggested the board’s assessment of fair value at GBP65 per share was overly optimistic.

The activist investor further raised concerns over the credibility of Intertek’s ongoing strategic review, which could result in a separation of the company’s energy and infrastructure division.

Intertek last week rejected EQT’s improved bid, stating that the offer undervalued the company and carried substantial execution risk. The company also noted that it had already attracted interest from potential buyers for its energy and infrastructure operations.

Neither Intertek nor EQT reportedly immediately commented on the latest developments.