A couple of questions

Northern Irelander said:

Gravity, plus pressure when hot

There will be a flow with the engine off, hot or cold

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I'm not necessarily disagreeing with you, he made the point that the flow responds to engine rpm though?

scarey said:

OK Thanks, what's the best way to flush out the rad?

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'Holts radflush' available from halfords.

I would expect the hose at the bottom of the radiator to be cooler than the top hose because the coolant would loose heat in the radiator, not so much when the vehicle is stationary, but still noticable.
You could have a blockage elsewhere so flush the whole system through.
I think NI is right to put his money on the pump, it must be overheating due to poor circulation.

Thanks all for the advise, I will flush the whole system and hose through the rad. Unforutnately nearest motor factors is over an hour away with Halfords 2 hours so will try with just water to start. Hopefully this will do it if not I will look at the pump.