Still haven't managed to stop the leak :-(
Took the hose off again at the weekend. The clip was plenty tight enough -- it looked like it was digging into the rubber. Examined the radiator outlet carefully for signs of a crack but found nothing. Made sure the outlet pipe was clean - even smoothed it with fine emery paper. Tried smearing some Fernox leak sealant compound (similar to silicone sealant) on the outlet before fitting the hose. It still leaks!!!!
I'm running out of ideas.
There does seem to be a fair amount of pressure in the cooling system when I release the radiator cap after the engine has been running for a while. Could it be that the head gasket has gone? If that were the case then surely the excess pressure should be released through the valve in the radiator cap rather than blow out through a hose joint?