Peter Johnson wrote:

Acrylic gloss is only fit for interior use at present. Decorators like
the acrylic undercoat (or often acrylic primer undercoat) because it
means they can get two coats (undercoat and gloss) applied in a day
and the gloss can dry overnight.

Most of the sheds do acrylic gloss branded as Stay White or somesuch.
A nasty synthetic shine, not unlike a plastic bag, with virtually zero
resistance to wear and bad adhesion to surfaces that aren't perfect.
However, it doesn't yellow with age and looks fine from a distance so is
ideal for stuff you need a ladder to get to.
I use acrylic undercoat all the time but usually topcoat with oil based
gloss. The only way you can tell the products apart on the shelf now is
the "quick drying" label, oh and the price.