Two Large Ones.
I may be wrong but:
Archie gives Tank 'Two Large Ones' as a livener to help him find the painting. It's barely a bundle of notes. It's about half and inch to an inch thick.
One Two kicks over the 'Two Large Ones' that they owe Lenny, to Archie, and it's a big heavy bag.
Is Two Large Ones two grand, or two million? Or does it change? Maybe Archie handed over a load of £100 notes, while One Two paid Archie in fivers? Pound coins even?