Recorded coworkers conversation at work? England

Hi,

I’ve been feeling mistreated at work for quite some time but kept trying to work through it and convince myself that it was all in my head.

I’ve worked there almost 2 years.

I’d just had enough. When I went to the toilet I left my phone on the desk with voice memo on. I listened back to it when I finished work and all of my suspicions were true, my coworkers were saying horrible, awful and untrue things about me. One of my coworkers was actually one of my best friends who got me the job, a bit heartbreaking really.

Obviously I’m going to hand my notice in to relieve myself of the stress of working there, but they are going to ask reasons why. I’d love to go into detail about all the things they have said about me, and complain to higher management/hr about these people but I’m not sure if revealing how I know about it would land me in legal bother? Or shall I just walk away and say nothing?

Thanks