Bank of England £20 with Green Dye

I have 2 £20 B.O.E Notes that have a Green Dye mark on the bottom left hand Corner both have it in the same Location.

It looks to be from the press but I'm not Shure. Has anybody else seen this on B.O.E Notes. 

I have seen the same denomination note with a blue dye. Not sure if still with me or used for shopping

BluHawk

I have seen the same denomination note with a blue dye. Not sure if still with me or used for shopping

Thank you its now been put to a good Cause.