Former Barclays director Baroness Wheatcroft told BBC News that Mr Agius was currently "carrying the can" but said Mr Diamond's resignation was now "inevitable".
Ian Wheatcroft, branch manager at Ciceley Commercials, in Petersfield Road, said some staff at the firm used vans to make short journeys around the site to avoid being "dive-bombed" by the birds.
However, Mr Wheatcroft said while some businesses could afford to pay for pest control, others could not and if individual companies tackled the issue the birds would only move on elsewhere on the estate.