Fitting Radiator Termostatic Value but Unsure If I can Unscrew old one?

[lockierp]

I've been doing some work to improve the efficiency of my heating system, which has involved replacing a few thermostatic valves. Easy enough, but i'm mystified by one radiator, which has no valve, it appears to have the valve connection to the radiator, but then just a simple turn handle, with a screw on the top. (can't figure out how to post the picture). It's just marked "scottish gas", and has an arrow for "open". The problem is, I think it's broken as the radiator is always on full blast. Can I just unscrew it and replace it with a proper thermostatic value. I don't want to just go and disconnect it, in case it has some significance! It's the only one of this type in the house.

Cheers