The bitter wrangle over the remains of Marconi moved towards a conclusion on Wednesday as the hedge fund holding the key to the £346m ($646m) sale of the business cast its proxy vote against the deal.

The decision by Polygon, the hedge fund, to block the agreed acquisition of Telent, the rump of the Marconi telecoms equipment company, has angered management and fellow shareholders.

An extraordinary general meeting on Thursday will determine the future of Telent. But barring a dramatic appearance in person of Polygon’s managers, last night’s negative vote will strike down the offer of Fortress Investment Group, the US private equity firm.

Mike Parton, chief executive of Telent, made a public plea on Wednesday for Polygon to support the deal.

“This is the only offer on the table,” Mr Parton said.

Telent issued a statement pouring cold water on the theory that a purchaser could lay its hands on the £490m held in an escrow account to secure the company’s £3bn pension fund.

The statement appeared designed to caution Polygon against the belief that there was more value in the company than Fortress’s offer.

Polygon is understood to believe that there is more value and had wanted to extract a higher offer from Fortress or to form a consortium with it to buy Telent.

Both these options appear to have been ruled out.

Fortress has said it will not increase its offer while the parties have taken soundings from the UK Takeover Panel to find out whether Polygon would be able to join the bid at this late stage.

The panel is understood to have advised that such a move would not be allowed as it could set a dangerous precedent, allowing other large shareholders to muscle in on offers on terms that are not open to other investors and damaging the central principle of shareholder equality.

Shares in Telent fell 6p on Wednesday to 490p, well below Fortress’s 529½p-a-share bid. The shares have fallen steadily in recent days on the expectation Polygon will vote against the deal and no other bid will emerge.