At approximately 7.20pm on Tuesday, 10 August police were called to an address in Tabard Street, SE1 due to concerns for the welfare of a resident.
Officers attended along with armed officers from the Met Police SO15
Following a search of the property, two items believed to be hand grenades were discovered. Firearms were also found.
Neighbouring properties have been evacuated while the items are assessed and dealt with.
The male occupant has been arrested on suspicion of firearms offences and remains in custody.