If you register at a certain company (PM and I will tell you) and get yourself a 0844 number, set your home number on the site so when you dial 0844 it goes to your home number.
give the withheld person your new number (0844) but do not answer the call. (you can answer too)
You will receive an email with the real number of the person that was calling. this works with all numbers from withheld, switchboards, call centers and international, so no matter how hidden their number you will always know who called you.
if you want to test it for yourself, pm me i will give you a test number, you can dial it and see its worth...and its free to use, setup and everything.