The chairman of Chime Communications apologised for the distress caused to 'friends of the company and staff' during the past week, but insisted the affair was a 'manufactured furore'.
He was particularly scathing of The Independent, the newspaper that printed last week's undercover expose of a meeting with Bell Pottinger after journalists posed as members of fictitious Uzbek firm Azimov Group.
'The methods used by The Independent and the Bureau of Investigative Journalists were underhand, unethical and improper, and their reporting of the matter had been partial, not even-handed, and deliberately slanted. Because of this, I will not respond to any other allegations from The Independent as I do not trust it to be fair and balanced.'
He insisted that he was taking the matter 'very seriously', particularly as he claimed that The Independent had subsequently contacted a number of Bell Pottinger clients 'in order to continue its campaign'.
Bell also argued that the three senior executives ensnared by The Independent were 'indiscreet and careless' rather than saying anything 'that resulted in improper actions'.
He wrote: 'I want you to know that I do not take these allegations lightly. We have instituted an internal review and will take action following that analysis and investigation.'
Chime's share price fell marginally on the back of the allegations, but more significantly has dropped by about 45 per cent since the start of June.
Last month, Chime said it was embarking on a cost-cutting programme after key contracts with the US government ended prematurely.
Bell added: 'I regret that this fuss has occurred, and I am upset at the damage done to our reputation and the well-being of members of our company ... It is not acceptable for a leading company such as ours to behave at anything other than the highest standards.'