Gor Blimey is a Cockney expression. It is a corruption of the phrase "God Blind Me" and is usually an expression of amazement.

Oh My Ol' Man's a dustman, 'e wears a dutsmans 'at
'e wears Gor Blimey trouziz and 'e lives in a council flat.
'e looks a proper 'nana in 'is great big 'obnail boots
'e's got such a job to pull 'em up that 'e calls 'em daisy roots.

The song takes it's name from an earlier Music Hall song which went something like...

My Old Man's a dustman - Whadderya think of that
He wears a dustman's trousers and he wears a dustman's hat
He talks a dustman's language - Whadderya think of that.

The family of the author of the original song filed a copyright infringement suit against Lonnie Donnegan, which was settled out of court.

The trousers would usually have been grey woolen gaberdine and would have been worn with 'knee irons'. That's pieces of string tied around the leg at or above mid calf with the trousers pouched out a bit above the string somewhat like plus fours.

Bert.