That would be notifiable as you are making a change to the CU, but I don't see why it wouldn't be possible. Lower rated MCB (16A) at the CU and double check the cable size. Just because it was running a shower, don't trust that it is correct unless you put it in yourself. As @Airhead said, it would likely need to be 2.5mm2 to be able to safely run power to the sockets without overheating, especially if it's going through/under insulation. You'll likely want to make sure you've gotten rid of any potential switch line to the shower too, lest you end up making that live when wiring up the socket.
That would be notifiable as you are making a change to the CU, but I don't see why it wouldn't be possible. Lower rated MCB (16A) at the CU and double check the cable size. Just because it was running a shower, don't trust that it is correct unless you put it in yourself. As @Airhead said, it would likely need to be 2.5mm2 to be able to safely run power to the sockets without overheating, especially if it's going through/under insulation. You'll likely want to make sure you've gotten rid of any potential switch line to the shower too, lest you end up making that live when wiring up the socket.