Green’s Dictionary of Slang

conkers n.

the testicles.

2000

M. Manning Get Your Cock Out 80: He [...] rammed his gristle up to the conkers in Delilah’s big fat arse.

In compounds

conkers deep

having the penis fully within the vagina.

1999		Roger’s Profanisaurus 3 in Viz 98 Oct. 9: conkers deep adj. To be in a state of total intromission. ‘Titania was powerless to resist. His eyes burned into hers like sapphires. His strong arms enfolded her tender body as she felt herself being swept away in a whirlwind of passion. Within seconds he was conkers deep.’ (from ‘The Lady and the Officer’, by Catherine Cookson).
2000		P. Howard Miseducation of Ross O’Carroll-Kelly (2004) 202: In two hours’ time I’m going to be conkers deep in this one.
2004		P. Howard PS, I Scored the Bridesmaids 113: Bet he’s buried conkers deep in some cracking bird.