"I can prefer the Birds custard powder to a tin ... but mostly opt for the tinned stuff, often through laziness..."

I thought the custard powder was for people who are too lazy to make custard using milk/cream and eggs.

When I was a child we used to go to Weymouth, and along the beach at the pebbly part there was a place where you could get trays of tea (proper cups, no plastic) and ice cream that smelled and tasted like Birds custard. Maybe that's what they made it out of.