Nikon would be around 300-600 Pound depending on model.
So at max that would leave 900 Pound for the lens, and for racing, air you'll need it.
Prob at least a 200mm with a f/2 diafragma, tho Nikon ones are in the 2000-3000 range
a fixed zoom lens would be around 500 Pound.
So might i suggest getting a D3100 that has a 18-55mm VR lens and buy a fixed zoom one.
Specialy for sport you'll need all the light and shuter speed you can get.
Canon are better if you want to take video on it as well.
For that you take Sony A65 hands down. Just because of autofocus.
Also video quality is higher on Sony A65 vs Canon 60D, 1080/60p vs 1080/30p.
You can take longer clips with it too, 29 minutes vs 12 minutes.
If you are willing to spend cash on 5D Mark II then that's another subject.
Canon is these days a supermarket stuff. In Finland barely any studio/photostore sell Canon anymore.
Yes we have 2x 5D MkII (Soon to change to 5D MkIII) as outdoor equipment but that's pro stuff.
In entry level everyone has passed them.