'Buttering your parsnips' is English, Bobby
Since when is the phrase "wouldn't butter your parsnips" not English?
"(You BUCKETTS, and WOODFORDS and COOPERS and others,
Whose names he need hardly string into his rhymes,)
_Punch_ hopes you may look on this Record sometimes
With pleasant reflections. Mere words, he well knows,
Will not--"butter your parsnips"--(to put sense in prose):
But you have his hearty good will, and you know it,--
Right gladly he takes this occasion to show it!
And when or wherever _another_ should come,
Be sure your friend _Punch_ won't be careless or dumb!"
From: Punch, Or The London Charivari, Volume 102, March 19, 1892
ftp://ftp.it.net.au/mirrors/gutenberg/1/4/3/6/14365/14365-8.txt