Peter wrote:

I have tried all the solvents I can lay my hands on but can't find any
that will remove burned sugar syrup from the white enamel metal
surface of the cooker.

Any remedies?

How good is the enamel? How fluid was the syrup when it got on it?
Depending on both factors it may dissolve with water or commercial
cleaner, it may also have marked the surface or cracked it, glass topped
hobs can be wrecked by molten sugar cooling....