The co-operative Group has taken on just 150 out of more than 1,000 staff at Somerfield's head office in Bristol, following its £1.57bn acquisition of the grocery chain last year.
The Manchester-based Co-operative Group always planned to close the headquarters of Somerfield, to deliver cost savings. But the exact scale of the compulsory redundancies has not previously been revealed.
Of the original 1,022 headcount in Bristol, 613 Somerfield staff have already left.
Most of the remaining 259 ex-Somerfield staff who are still working at the head office will have left by Christmas, although 60 will remain until June 2011 to support the handover of systems. Ultimately, the Co-operative will have made 872 out of Somerfield's 1,022 head office staff redundant and property agents started marketing Somerfield's head office building last week.
The Co-operative Group said the process had been conducted in "full consultation with the unions concerned". A spokesman stressed that consultations with Somerfield staff started in June 2009 and some of the head office staff found other jobs without waiting to see if there was a job with the enlarged group, sometimes because they did not want to relocate the 140 miles to Manchester.
A spokesman for Usdaw said that while it regrets the loss of jobs at Somerfield's head office, the shopworkers' union has "no issues with the very thorough consultation process the Co-operative Group has undertaken with the individual staff concerned".
The Co-operative's acquisition of Somerfield created the UK's fifth largest grocery chain, with more than 3,000 stores. Some 27,000 Somerfield store staff were taken on.
A spokesman for the group said: "We have been utterly transparent from the outset regarding the need to make the most of synergies and implement a cost-effective structure for the enlarged business, the fact that we would close the Somerfield HQ, and that while we would try our best to accommodate as many people as possible, it was never going to be possible to take everyone."
The group has denied the integration of the two businesses is proving more difficult than expected.
A leaked board report dated 20 April revealed that Somerfield's sales had plummeted for the year to date. But the company insisted that Somerfield is trading in line with expectations, partly attributing the fall in sales to the fact it had lowered its prices.