HELP - buttermilk substitute?

[CardiffUniversityNetballTeam]

I have bought all the ingredients to make a red velvet cake to take to my mums on Boxing Day. Except for buttermilk which I can't find in any local supermarket or shop. Can I use normal milk instead?

"There are a number of substitutes for buttermilk in baking. For each cup of buttermilk, you can use 1 tablespoon of white vinegar or lemon juice plus enough milk to measure 1 cup. Stir, then let stand for 5 minutes. You can also use 1 cup of plain yogurt or 1-3/4 teaspoons cream of tartar plus 1 cup milk."
google says

I have added lemon juice to milk and it has made ok buttermilk.

Sainsburys sell buttermilk in the cream section

I use half milk half plain yogurt to replace buttermilk.