Hi, I see your from the UK too. One of my males is being exactly the same way. I can tell you from my experience ( he's a mouser) that having a male, who eats sporadically on mice, is one big worry sometimes. He will rarely eat two...

The mice sold are quite small, unless you're purchasing xl (retired breeders) mice. Have a look into multis, a lot of people are breeding them over here now. I would sooner feed multis/rats than mice, to my males at least...unless of course I was breeding my own mice.