Overheating problems diong my head in!!!!

We recently got a 1.8 Golf (1989) and are having difficulty in keeping her temperature down.
I have replaced the thermostat, also the thermoswitch on the radiator.
It was working fine for a while and now has decided to heat up again.
The coolant is circulating as I see it returning to the expansion tank, but now the fan hadnt cut in or the thermostat opened(I think as the top hose was hot and bottom one freezing!).
Also temp stays high and increases as I am driving, even above 45 mph.
Is my radiator dead?
Could the temp sensor be at fault or is there something I am missing.
The car also idles fast unless I blip the accelerator and the she idles at about 1200 rpm, also runs on a bit after switching off engine.

Could use some decent advice please,
Many thanks

If the top hose gets hot & the bottom stays cold then there is a circulation problem. If you're sure the t-stat is good & the water pump is pumpung (evidenced by the bypass flow into the expansion tank) then suspect the radiator is clogged.