Officers had gone to a private address in Elm Park Avenue, Hornchurch at 18:10hrs on Sunday, 24 January. Inside they found 20 guests from a number of different households.
Those attending ranged in age from young children, to teenagers, to people in their late 40s.
After seeing the gifts and balloons, it quickly became apparent to the officers that the gathering was not spontaneous and the two organisers – men aged 22 and 44 – were reported.
Others involved were advised and left the premises.
Chief Superintendent Stephen Clayman from East Area Basic Command Unit, said: “This gathering had people of widely different ages and from different households present. Whilst I fully understand that people want to get together to celebrate events, this is definitely not the time to do it in person.
“A gathering like this can have tragic consequences for all those involved and risks spreading this terrible virus to our loved ones and the wider community. Please have no doubt, we are determined to deal robustly with those who breach the Covid regulations in this way.”