Shares in TDC fell on Monday after the company’s biggest shareholder said on Sunday night it would not accept an agreed $12bn cash offer for Denmark’s largest telecoms operator from a consortium of private equity groups.

ATP, Denmark’s biggest pension fund, owns 5.51 per cent of TDC. Its move could threaten Europe’s biggest ever private equity acquisition if other shareholders follow suit. “This was a pure investment decision,” said Bjarne Graven Larsen, chief investment officer at ATP.

The fund, which says TDC could achieve a higher valuation as a listed company, has not been in touch with any other TDC shareholders prior to deciding not to accept the offer, he said. Some Danish small investors have also expressed scepticism about the offer. Altogether 15 per cent of TDC is owned by private investors and employees.

The offer for TDC was made in November by Nordic Telephone Company, which comprises private equity groups Apax Partners, Blackstone, Kohlberg Kravis Roberts, Permira and Providence Equity Partners. The DKr382-a-share offer has been recommended by TDC’s board.

Both TDC and NTC released stock exchange announcements yesterday morning encouraging investors to accept the offer. TDC said it was confident it would achieve the required minimum 90 per cent acceptance level.

NTC declined further comment. However, it placed an advertisement in a Danish newspaper saying: “Dear TDC shareholders, we would very much like to buy your shares.” The deadline for the offer is January 12. The consortium can, however, extend the bid period.

TDC shares fell 6 per cent on the news before recovering to close 2 per cent lower at DKr370.