Even modern rads will silt up and become inefficient after about 10 years or so. Regular flushing and use of inhibitor will help to extend the life of a system. Best bet is to simply replace your older rads with new ones. Try to get the same sizes to minimise pipework alteration. Powerflushing a...
If you dig it up you mustn't leave any bits - even an inch - as it will grow back. In fact this may help it spread. Weedkiller will work but over several years from my experience.
It has been used as animal feed - maybe get a goat?!
Is there an electric tool that will cut the centre from a ceramic tile (eg. so that it is left looking like a 'U' shape) or do I need to use a hand saw?