Green’s Dictionary of Slang

a general intensifier; esp. as stonking great...

1995		I. Rankin Let It Bleed 97: She made [...] a ‘stonking good witness’.
2004		G. Macdonald England 516: Boulton made things out of metal: small things like buttons and buckles [...] and stonking great industrial steam engines.
2009		H. Phibbs Guardian 16 Mar. 🌐 But what about the public sector’s own stonking great carbon footprint?