Bim’s Burgers, in Ilford, was hit with the penalty charge after police found it had allowed a single customer to order at exactly 10pm and passed over the food 240 seconds later.
A spokesperson for the restaurant said that, given the customer had started placing the order ahead of the nightly curfew, staff believed serving them fell within the law.
“New rules regarding Covid-19 are being made thick and fast and sometimes it isn’t clear exactly how they should be interpreted,” they said.
The fine was one of many given out across England as the country entered its second weekend with the new curfew and table service-only rules in place for pubs, restaurants and other leisure venues.
In Liverpool, one nightclub was hit with a £1,000 levy after police found not all customers were seated and several were not adhering to social distancing rules.
The venue, 24 Kitchen Street, was raided by officers at 8.30pm on Friday following reports.
Chief Inspector Karl Baldwin of Merseyside Police said: "It is extremely disappointing that for the second weekend in a row we have been forced to issue a fine because a premises has failed in its obligations to act responsibly.”
Meanwhile, it was revealed on Friday that a hotel manager in Solihull became one of the first people in England to be hit with the maximum £10,000 fine for breaching coronavirus regulations after hosting a wake with more than 200 guests.
Castle Bromwich Hall Hotel was handed the penalty after West Midlands Police were called to reports of the huge gathering on 25 September.
The venue has also now been banned from holding any events until January.