right, I have just done a few more tests on the car:
First I checked the coolant level, it was very low, needed over 2 litres of water to top it back up to full.
Once I had done that I let the engine idle for a bit and as soon as I turned the key in the ignition the temperature guage shot right up to the very top way past the red line. Obviously the engine cannot have been that hot straight from startup.
After a couple of minutes the temperature fell right down to just under 1/4 and then it rose again to about 3/4, eventually it settled down to just under a 1/4 after 5 minutes.
The temperature coming from the heaters on full was again 'vaguely warm', but if I increased the revs to about 3000rpm the air coming from the vents became noticeably hotter almost instantly, and when it went back to idle again the temperature again dropped.
Another thing that I noticed was that the radiator fan came on straight away, should this only come on once the engine has reached its' operating temperature and needs to cool?
Anyone got any bright ideas as to what the problem could be then? All responses very much appreciated!