If he makes some sort of point of picking up the £1 chip and placing it with the £25 chip then it's a raise. Or if he taps the £1 chip with the £25 chip and leaves it in or something then it can be taken as a raise.
But in general it's just going to be a call.
Pretty much this for me too. This is how Id call it 100% of the time.
People leave the chips they have in the pot in there all the time in this situation because either a) theyre too lazy to reach and get it or b) they forget its in there. Are you going to make every single person that does that raise?