Traders claim they lost tens of thousands of pounds during a bank holiday power cut because an energy firm lost keys to a substation.
The five-hour loss affected more than 230 customers in the High Street area of Littlehampton on August 23 last year, causing dozens of businesses to lose trade totalling £50,000.
Business owners say UK Power Networks (UKPN) initially told them the reason for the prolonged disconnection was because of “faults” in the power lines.
But it has since been revealed UKPN could not re-connect the power sooner because its engineers did not have keys for a substation.
Andy Sparsis, of Proto Restaurant Group, which runs Fish Factory in Littlehampton, said: “The reason it was so severe is because it was a bank holiday weekend.
“All the traders phoned UKPN and were told it would be back on within two hours, so people shut business down and put signs in their windows.
“They put the power back on after three hours but by that point only one phase went back on. In commercial businesses there are three phases of supply. When you only put one back on it’s like putting diesel into a petrol engine.
“Because of that loads of traders had small explosions, computers blew up and our main freezer went, costing us £3,000.
"The power went off again and stayed off for hours. We had bookings at restaurants and had to cancel everything. They effectively shut the town down.
“An engineer told us they’d lost the keys and that’s why it took so long. It’s unacceptable and cost us thousands.”
Nigel Croad, resources director and deputy chief executive of Arun District Council, said the authority was keen to support residents and businesses when “matters like this occur” and asked the firm to find a “fair resolution”.
But a UKPN spokesman said the firm was only obliged to give compensation to customers when electricity supplies were disconnected for more than 18 hours.
He said: “In this instance access to the relevant substation was reliant on a long-standing, dual-locking arr-angement with another organisation needing access to the same site.
"However, a new tenant, not understanding the arrangement, had removed the dual-locking system without our knowledge or approval.
“Two of our Sussex area managers met traders and officials of Arun District Council earlier this year to discuss the issue.
"We told them that new arrangements have been made with the sharing tenant, with our properties department researching access options that would not involve a dual system.”
The firm added its customer services director had last week written to businesses apologising for the incident and would arrange to meet with traders and council bosses.