Hiya, Linda (as we say in Manchester!)
My reaction was the same as Paul's. Let me explain. The northern part of (the island of Great) Britain is Scotland, where people - not surprisingly - have Scottish accents. So the idea of a 'Northern British accent' doesn't make any sense.
Manchester is in Northern ENGLAND, not 'Northern Britain'. Perhaps you could try asking for an English person with a Northern accent?
We're also rather confused about your choice of adjective to describe yourself. First you put 'constant' (which was strange), then you changed it to 'consistent' (which is even stranger). What exactly do you mean? If you can explain - or even tell us the word in Spanish that you're trying to translate - we can perhaps suggest a better word. Do you mean reliable, perhaps?
Good luck with your search, by the way.