issues with a bleed valve (radiator removal)

Hi all. I can put my hands to most basic things DIY, but am terrible at anything plumbing related. I have moved into an old victorian property, and the radiators don't look in the best shape. I am currently trying to remove a radiator so I can strip the wall behind, but I am having some problems.

I turned the spindle of the lockshield valve clockwise until it stoped. I was advised that I should then loosen off the bleed valve to allow the radiator to empty. However, when I did this, there was a strong steam of water coming from the bleed valve. I directed this into a bucket - expecting that it was just the water at the top of the radiator and it would soon subside -but it kept on coming!

Am I approaching this wrong, in that I am bleeding at the wrong stage? Or could it be that the radiator valve is broken (hence why the water didn't subside after a couple of minutes)?

The radiator also has what was once was a thermostatic radiator valve, althought the top is missing. I'm not sure if this matters...

Any help would really be appreciated! Thanks, Chris

The radiator will not shut off if the head is missing from the thermostatic valve. You get a special plastic cap with the valve when purchased that you screw on the valve in place of the head.
You could take a head from another radiator, presuming that they are the same but be very careful as the heads are designed to open if the temperature drops below a set point, even if they are in the off position.
This is very likely in this cold weather.
You would be safer to drain the system if you do not have the cap.
Steve