I’ve just been doing a bit of research. They will definitely fit 25mm tyres. Apparently 28s will just about fit too.
They are certainly a slightly retro, aero fork made for TT and track bikes so the clearance is not huge. I will do some more googling, and when I have time in the next few days I will do some experiments of my own.
Hope that’s helpful!
Edit: further research suggests 28mm will fit, but probably no bigger. Of course not all 28s are exactly the same size, and rim width etc makes a difference too, but sounds like 28 should be ok