"New" (post 91/92) English copper coins are not made of copper or silver. Neither of them being magnetic. They're made from copper plated steel. They've been made of steel since September 1992.
The reason that they're made of steel now is that it's a lot cheaper than base metals such as copper, zinc and tin.
And as for the other bit... If a piece of lead can stop gamma rays from getting through it, I can imagine it would stop a high percentage of magnetic rays. Could be wrong though!
Also, if you're wearing lead anywhere on your person,be careful you don't cut yourself with it

You wont find much better anywhere and it's nothing - a rigmarole with a few bits of paper and lots of spiel. That is Mentalism
Tony Corinda