Planning to leave my job but still have holiday hours

Hi everyone, in England (born and bred if that matters) I've worked for a retail company for over three years now, and I'm planning to hand in my notice at some point soon as I'm getting sick of it and I've potentially found a better job opportunity. In my contract it says I have to give a weeks notice for every year I've worked there, so I'd have to give three weeks, which I'm fine with. My issue is I have holiday hours built up, they're based on how many hours I work the previous year, and I have some booked for next month but I have some I haven't used, I have 67hrs to be precise left to use to book days off, if I hand in my notice before I've used or booked any holiday will I still get the equivalent pay for them, or will they just go completely? I've looked this up and I've seen mixed things and thought it'd be best to ask here. Thanks in advance