Good luck on that budget. I'm not sure a tri-pod is ideal for wildlife tbh. I can use my tripod as a monopod as well, but I could not get the hang of it. I have a ball head, and I think you really need a gimbal if you want to go down the whole tripod-wildlife-heavy lens route.
The gimbal I'm looking at is upwards of 400€ and it really is one of the cheaper ones.
I always see these sport photogs with their monopods, so I guess I will have to practise some more.
Fancy chucking a link to your current tripod and that gimbal you have been looking at?
I don't know what this is in £
but I have this and it works well, when I use it. I rarely use it now.
Amazon.com : Opteka GH1 Professional Heavy Duty Metal Gimbal Tripod Head with Arca-Swiss Standard Quick Release Plate (Supports up to 30lbs) : Tripod Heads : Camera & Photo
If you think about movement of the subjects you want to take a picture of you can guess how useful a tripod/ballhead is versus a tripod/gimbal head vs a monopod vs handholding.
Let's say you are a distance from large birds. And those large birds are flying left to right.
A gimbal or ballhead would work fine.
Conversely, if those birds are flying directly at you and overhead.
as they approach your lens goes up, camera down. Now how do you aim? Through the viewfinder or a flat or tilting LCD ?
Do you continue to take pics as they are directly above you ?
If so, how ?
Do you move around often, or sit in one spot?
Think of what you take pictures of, and how their movement is to your position, etc.
As to price, you'll have to decide to go carbon fiber (really expensive) or aluminum (much less expensive). And normally the fewer leg extensions the better, but then the less portable in size. Pick one brand, such as Benro, ManFroto , etc and learn about their entire line and learn what makes a $700 tripod $70o dollars?? Then compare to other brands.
I think Anything under $200 USD /$155 GBP can be considered questionable in sturdiness especially for large lenses.
Next time you see other photogs with tripods dont' just look at the camera/lens. Looks at their tripod setup.