Police officers were tipped off about the bash by a member of the public who had noticed taxis bringing around a dozen guests to the venue, above shops on Erdington High Street, at around 11.30pm yesterday.
Once inside, our officers found a DJ, disco lights, beer, birthday cake − and even Class A drugs.
WATCH: Partygoer answers door in dressing gown
Around 50 people were found there and fined, while the suspected organiser was arrested after refusing to give their details. They could now face a fine of £10,000 under coronavirus legislation.
Meanwhile, officers responding to reports of a house party in Kings Norton at around 12.30am today spotted flashing lights and heard music coming from inside.
The lights went out when they realised officers were outside, and a woman came to the door in a dressing gown.
After being questioned as to why she was wearing jewellery and fake lashes to bed, she showed officers inside the flat − where police were told a party was being streamed live on Instagram.
Some guests were allowed to leave but three people were arrested after two officers were assaulted.
More than 300 lockdown fines have been issued this week, including around 70 given out at an illegal nightclub in Birmingham.
ACC Chris Todd said: “Our officers don’t get any enjoyment out of spoiling people’s fun. They are simply trying to keep people safe and reduce the spread of the virus.
"Where one person might be asymptomatic with the virus, the next might become seriously ill or worse. People who go to these events need to know that they could be spreading the disease without knowing it, or even picking it up while they are out and then bringing it home to loved ones.
"These breaches are likely to prolong the duration of this pandemic for everyone. Most people are doing their bit, and we are grateful to them for making our jobs easier and saving lives."