As long as it's small enough for the worms to eat it should work in theory.
Or you could buy some of this and dip the back end of the worm in it or sprinkle it on cutup worms.
Not sure if this is sold in the U.K. but I'm sure there are products available that will do the job.

Amazon.com: Rep-Cal Calcium with Vitamin D3 (4.1 oz) Ultrafine Powder Pink bottle: Pet Supplies