The seven-man independent board is charged with making a decision on the mooted takeover of the Kazakh mining group as the deadline for a bid looms on 17 May.
The takeover is being led by the trio of oligarchs who founded ENRC and the government of Kazakhstan, who collectively already own 56 per cent of the firm.
The news of the takeover emerged after the Serious Fraud Office (SFO) instigated a criminal investigation into ENRC and allegations of corruption related to its African operations.
Brunswick, which declined to comment, is understood to be working purely for the independent board in the event a deal materialises, and not for the company itself.
M:Communications continues to be retained by ENRC and is handling day-to-day comms around the SFO investigation and other allegations of malpractice.
Last week a panel led by former UN secretary general Kofi Annan alleged that the company had cost the Democratic Republic of the Congo at least US$725m (£612.2m) in potential revenues between 2010 and 2012 as a result of undervaluing state assets.
Felix Vulis, chief executive of ENRC, told investors last week that ENRC was 'co-operating fully' with the SFO investigation.
Morgan Stanley and Deutsche Bank have stepped down as the company's corporate brokers in recent weeks, but M: said it had no plans to resign the account.
ENRC raised £1.5bn when it listed on the London Stock Exchange in 2007.
However, the shares, which floated at £5.40, were trading at about £2.30 before the takeover bid was announced.
The Takeover Panel gave the takeover consortium a deadline of 5pm on 17 May to make an official bid or walk away from negotiations.
Media reports suggest the company's founders will seek an extension to the deadline.