Green’s Dictionary of Slang

a general term of approval, enormous, excellent etc.

1999		Indep. Rev. 3 July 17: Stonking steaks, burgers, ribs, and pecan pie.
2000		Guardian Weekend 8 Apr. 3: They’ve got me mixed up with some stonking old party girl.
2014		Guardian 4 Mar. 32/4: Zaha Hadid’s creation for the 2102 Olympics was praised [...] as a stunning building, one critic describing the interior space as ‘stonking’.
2018		Eve. Standard (London) 20 Aug. 43/1: ‘Brinks’ has won a third, worth a stonking £800,000.