Notes: Wallington is (lovely) place in Northumberland, 'Fairly shot of' means 'well rid of'
Slip jig is the term for jigs with a 9/8 time signature (diddly diddly diddly) instead of the more usual 6/8 jig (diddly diddly). Northumberland has developed its own variant of these tunes, based on the distinctive characteristics of the Northumbrian Pipes - tunes with an emphasis on arpeggios (broken chords), and a tendency to staccato articulation.
Also distinctive is that these slip jigs 'end' on the dominant chord; which means they don't really end but either stop abruptly, need an additional tonic chord, or else they seem to want to go on and on, round and round, forever.
These (especially Drops of Brandy) are the favourite tunes to play at the end of the 'ceilidhs' (barn dances) which are popular here, since they accompany the traditional final dance of the evening - 'Strip the Willow'. Which may be so vigorous that (when over-excited or unskilled men are involved) it can be dangerous; my daughter was at such a dance when two of the girls were taken to hospital afterwards having suffered significant injuries from being swung too hard, fast and often.
The dance has a hop-step movement, which means that it syncopates across the bar lines for a 9/8; each 'diddly' being either a hop or a step, making two diddlys per bar which has three diddlys - and therefore the order of hopping and stepping within the bar is different for each adjacent bar.
That's how it 'works' musically; but, anyway, in practice such syncopation probably accounts for some of the almost magical, elated feeling when dancing Strip the Willow to slip jigs.