If a bailiff enters the common hallway of a housing block, but not my flat, is it a peaceful entry?

Yes

But this does not grant a right to break entry to the debtors flat.

Bailiffs can gain entry to communal areas of apartment blocks by waiting for someone to enter or leave, or pressing the tradesmen's buzzer.

If the debtor keeps goods in the communal hallway, the bailiff may take control of them.

If a bailiff causes a disturbance in a communal hallway to coerce someone to open a door to one of the flats, they should call the police on 999 reporting a suspect on the premises.

If the door to the flat is opened, the bailiff may deploy the threshold maneuver,^[1] and force his way into the flat.

^{[1] See Bailiffs putting his boot into the door to stop it being closed}