Immigration lawyer Harjap Singh Bhangal has told talkRADIO that Byron Hamburgers had "no choice but to cooperate" with the law after they helped to deport illegal-migrant staff last month.
Byron Hamburgers has endured a storm of criticism in recent days after the chain took part in a sting operation to help the Home Office catch migrants with false work permits and residence papers.
On Friday night, radical activists from The London Black Revolutionaries and the Malcolm X Movement released what they said were 8,000 crickets, 4,000 cockroaches, and 1,000 locusts in front of bemused customers, shutting down two outlets in Central London.
The protesters insist they will 'bankrupt' Byron if the company does not apologise for the part they feel it played in the deportations, but Bhangal says the restaurant chain has nothing to apologise for.
"It's a legal defence if you're presented with fake documents and you believe them to be genuine," he told Julia Hartley-Brewer.
"The fact these documents are available, that's where the system is failing.
"If Byron Burgers acted appropriately, why should they get fined or be duped, or fall foul of the law? It doesn't make any sense.
"Immigration would have [still] come in, acting on a tip off. They [Byron Burgers] were put in a corner, with a fine of potentially £750,000.
"They had no choice but to cooperate."
Listen to the full interview above