Mark Pignatelli, who runs European investments for the fund manager, was one of several London institutions who supported Olivetti after the company raised pounds 913m in a rescue rights issue last December.
Last week, he told a standing committee of the Italian parliament that "selling off Omnitel would be a mistake. Selling a share of value to sustain an investment soaking up money like Infrastrada [is wrong]." Olivetti would still be left with a majority stake in Omnitel.
Mr Pignatelli was infuriated by the prospect of another rights issue, which he dubbed a "terrifying hypothesis."
Infrastrada is the fixed-line telephone company in which Olivetti has a large stake. Its future is seen as limited by analysts in comparison to the high growth potential of Omnitel.
UK institutions were believed to have owned up to 15 per cent of Olivetti, following a rescue rights issue by the company last December - even though Italian banks and investors were quietly selling off their holdings in the company at the time.
ING Barings sat on a 6 per cent stake - at one point it was believed to own as much as 8 per cent of the company. Olivetti shares have fallen from over L1,000 (41p) in April to an all-time low of L435.
An Olivetti spokesman said: "We are doing all we can for shareholders. It would be nice if shareholders could give us a break and leave the board to get on with sorting out the problems."
Enzo Berlanda, president of bourse authority Consob, is understood to have handed a report to Turin's public prosecutor concerning Olivetti's share movements between the end of August and the beginning of September, before the company's first-half results. Consob noted that former Olivetti chairman Carlo De Benedetti sold stock in the company during this period.
Troubles at Olivetti escalated after its first-half figures in September, when it posted a pre-tax loss of L440.2bn.