PVA watered down 4:1, apply with a roller, it’ll take 15 minutes, stabilise any dust, (which will stop new paint adhering properly) and kill any suction, (which might save you a couple of coats). You can get a 2.5L tub in B&Q for about £6 that’ll more than cover a standard size room.
For such a small, inexpensive precaution and considering the existing paint has failed, it’s daft not to.