I've just got a brand new Youview box and have tried to tune it but only got 20 very random channels. No mainstream channels at all. When the aerial was put in a couple of years back everything worked fine but I've only been using my Sky box to this point. Unless I have done something wrong in assuming it's the aerial. To be honest it looks absolutely fine but I don't know.
Does it even matter once I get the Internet on?
The box needs a working aerial for the standard BBC/ITV/Channel 4 type channels. Only the extra pay channels are delivered via the broadband.
Do you have access to an indoor aerial you could try? They're not suitable for everyone because of signal strength but if you pick up more channels with that it would suggest am issue with your main aerial.