Golden Acre Park is quite nice. Free entry and free parking and there is a lot of wildlife; duck, bird, geese,ducks and flowers to photograph.
Tropical World in Leeds is also very good. I went there recently, but I didn't have my camera with me, and plan to go again. There are some lovely exotic butterflies and plants there. Great for macro work. A lot of things are behind glass, so they don't make the greatest of photos, but I still got some reasonable shots with my mobile phone.
It's £3.50 to get in. It's got children in, but it's worth it, and you could always go when it's not the school holidays. There is also a pretty garden with a lovely variety of flowers next door.