If you have a Samsung phone then there is call blocking built in. Think it's limited to their phone rather than being on all android but I may be wrong. If you have one of them you can block certain numbers or even all number that start or end in certain digits, so you can block all of say Manchester if you want
It can be accessed by long pressing a number in your call log or through the call menu's somewhere. Works so well you won't even know you missed a call unless you check the logs
Otherwise you need an app and I can't help there, sawwy!