There are no rules or regulations outlining a set distance a socket should be from a radiator.
However, you should consider the impact that the transmitted heat could have on nearby cables, wires and other electrical equipment. Therefore, a clearance distance of 150-300mm, or 6 to 12 inches, is recommended.
For further radiator fitting tips and advice, consult our how to install a radiator blog. Or, for inspiration surrounding the finest radiator models to select for your home, view our comprehensive radiator buying guide.