A rift between seven investment trusts and an activist investor has become more aggressive as the boards issued a series of statements defending their performance.

Boaz Weinstein, founder of the New York-based hedge fund Saba Capital, launched a campaign to oust the boards of the trusts on 18 December.

Saba has accumulated stakes ranging from 19% to 29% in the trusts, which include Baillie Gifford US Growth Trust, Edinburgh Worldwide, European Smaller Companies Trust and Keystone Positive Change Investment Trust.

In his pre-Christmas attack he said: “Performance demonstrates that they have not taken sufficient steps to resolve the trusts’ structural issues, depriving shareholders of superior returns.”

Three of them today responded with a firm defence of their positions and urged shareholders to vote against Saba’s proposals.

Baillie Gifford US Growth Trust, an £830 million listed fund, noted that a general meeting has been requisitioned at its offices in Greenside Row, Edinburgh on 3 February.

It accused Saba of proposing “substantial, self-serving and destructive changes to the company.”

Tom Burnet, non-executive chair, said: “Since IPO in March 2018, the company has delivered exactly what it promised: an investment trust through which its shareholders can access and benefit from some of the most exciting growth opportunities in both public and private US companies in a low-cost structure that can be held for the long-term.

“Accordingly, shareholders who invested at IPO in 2018 have nearly tripled their initial investment. Further, the growth outlook for our portfolio companies is extremely strong.

“Baillie Gifford’s global reputation provides it with preferential access to the US growth companies of tomorrow, so the future of this company is bright. Saba wants to subvert all of this.

“Their proposals lack detail and if implemented, could destroy the Board’s independence, radically alter the investment strategy of the Company and prove highly disruptive to shareholder value.

“We urge all shareholders to make their voices heard and to vote against Saba’s self-serving and destructive proposals.”

Edinburgh Worldwide, which manages £809m, accused Saba of “a backdoor attempt to seize control of the trust”.

Jonathan Simpson-Dent, the EWI chairman, said a valid requisition notice had been received from Saba and a date for a meeting would be announced soon.

He said the board would urge shareholders to vote against the proposals, and added: “Edinburgh Worldwide is an exciting and unique investment trust that offers unparalleled access to emerging companies operating at the frontiers of science and technology.“

Keystone accused Saba of “a flagrant disregard” for corporate governance standards. Karen Brade, chairman, said: “We are appalled by Saba’s actions and conduct.”

A spokesperson for Saba Capital said: “It is appalling that KPC [Keystone] chair Karen Brade has overseen cumulative underperformance of nearly 130% since assuming her role in 2018 – a staggering loss and destruction of wealth for retail holders and retirees.

“Contrary to KPC’s fearmongering tactics, Saba has an award-winning track record in closed-end activism that has provided liquidity, low fees and better management to deliver long-term value for all shareholders.”