In an emotive speech to retailers at Costcutter's annual conference in Barcelona, Graves said he was stepping down immediately after being excluded from board meetings. He also claimed Nisa had attempted to poach all Costcutter's retailers.
"For the past nine months, Nisa has said there's been a conflict of interest and I've been told I can't attend board meetings because of it," he told The Grocer afterwards. "In this situation, there's no point continuing. I've been on the board for 20 years and to be treated like that is unbelievable."
Costcutter would still honour its distribution agreement with Nisa, which runs until 2014, he said. "We have a contract in place and will continue as we have done."
However, he added: "We asked them to put a new contract on the table. They said we turned it down. That's completely untrue."
Nisa CEO Neil Turton said Costcutter had not accepted the contract, but said he was "keen they do". Graves was never banned from meetings, he insisted. "Last year, we had two hostile bids from Bibby, Costcutter's owner, and Colin clearly couldn't take part while the Nisa board talked about the bids," he said. "After the bids were turned down, Sir Michael Bibby said failure to acquire Nisa meant he would split Costcutter away from Nisa in the future. We needed to plan for all eventualities and took legal advice, which Colin was aware of.
"We told him he was welcome to stay as a director but there were parts of Nisa's board meetings where it would be sensible for him to stand out. He's been a director throughout, sent agendas and invited to all the meetings."
Turton denied Nisa had approached all Costcutter's retailers and said the only high-profile defection had been Red Orange which had moved to Costcutter.