mam's life

In the UK, typically somewhere like teeside, this is a phrase to say as a way to promise XYZ is the truth. Mainly used in secondary schools.

Dean: stop chatting shit about my dead nana ya specky cunt!

Mackenzie: what are you on about!?

I didn't say nish. What are you piping up for?

Dean: swear down then.

Mackenzie: mam's life I didn't say ought (out) about your nana, kid fuckin' hell man.