I not long brought a canon 550d.
I no it's cos I realised I posted the wrong post in where you introduce yourself, probably being half asleep don't help

You have a Canon? So you need 'the' safari lens, the 100-400.
Honestly, forget about 70-200 with a TC. You've paid a lot of money to go on holiday, get some decent pictures. Buy a second-hand 100-400 for £880 from MPB, use it on safari then flog it when you return for £800.
150-500mm from sigma you have long reach (but i don't think that optically they are very good)
Hi guys I have seen 2 lenses that I'm after that are in my price range and I have seen some good images on both of em.
The lenses are Sigma 120mm-400mm f4.5, sigma 70mm-200mm f2.8, or the tamron 70mm-200mm f2.8?
What people never tell you is just how dusty these places are, changing lenses all the time is a recipe for a filthy inside of your camera (the outside WILL be filthy whatever) I know this now...
I reckon a decent 300mm on a crop body is enough for pretty much everything
From reading about problems with dust, would it be advisable for me to take a camera cover.
If you go down the rent route then take a look at the Sigma 120-300 and a 1.4 convertor, that will give you a very flexible range with f2.8 for those early morning game drives.
I was thinking about renting the 100-400 lens, due to my budget being only £750
Dust is really only a problem when you're travelling. Once you stop moving the dust soon settles.
And some shots need to be taken on the move.