I have never heard the expression used by anyone in Hull!
Besides you said it is "Northern English"
Hull is in YORKSHIRE
(English is understood, but not spoken)
For the guidance of those less fortunates who are not actually from Yorkshire the Good old BBC 'Umberside have provided a handy guide
http://www.bbc.co.uk/humber/content/articles/2005/02/14/voices_hullspeak_glossary.shtml
This is by no means a comprehensive guide, many words like "Wassamarrawivyer" can be used as an interrogative.
You will note that the word "Mardy" is conspicuous by it's absence.
And a likely alternative to "Mardy" is most likely to be
Wassamarrwivyer, suffixed with Gotyerknickersinnatwistaboutsummat?
Which gives some idea of the sparkling wit and subtlety of the local patois.