Space for luggage overnight?

I'm going to London an my last day there is a overnight screening in a cinema that I'm interested, I though of extending my stay for an extra night at the screening but the cinema doesn't has a cloakroom

Is it safe to leave my luggage overnight at bounce or stasher? Any other places you recommend? I've tried looking for reviews but aren't too convinced of how safe it might be

I would really like to make it work so any help if appreciated