Hello Maciej
It looks like you purchased a device that was used on a production network, and they didn’t even bother to clear the configuration!! If the device truly belonged to British Telecom (BT PLC), then it is greatly negligent of them to keep their config intact. Best practice dictates that you should always erase all configurations before reselling such devices to prevent potential malicious users from discovering passwords, IP addresses, and other confidential company information.
In any case, if you want to recover the device, you simply need to perform the password recovery procedure shown in this lesson:
I hope this has been helpful!
Laz