I've been trying to replace the little valve in my toilet that feeds the cistern as its cracked at one side, I've turned the main stopcock off but there still seems to be pressure in the 15mm copper pipe, is there another stopcock somewhere

I've been trying to replace the little valve in my toilet that feeds the cistern as its cracked at one side, I've turned the main stopcock off but there still seems to be pressure in the 15mm copper pipe, is there another stopcock somewhere
Yes there is. If the house shut off is faulty you can shut the system down, if you're on city water at the meter. If you're on a well shut the pump off and bleed off the pressure by opening up a cold water faucet. Good luck, Tom