To be honest, if I saw those stats from your router, I would say replace it. Upstream errors are almost always faulty wiring or equipment, and if those stats are accurate, you are sending a lot of upstream errors, which isn't going to help anything. It may also explain the poor wireless performance, but it is a bit of a tenuous link, but may be indicative of a router on its way out.
If you have a spare router, try that, easiest way to find out 
To be certain, phone your ISP, and ask them to run a diagnostic. If they are vaguely competent, they'll be able to see the errors themselves, and can advise you accordingly.
Thank you for your comments.
It's a BT Home Hub 2 and is newly supplied. The CRC upstream errors are a bug - now they have a Home Hub 3 its unlikely that they will fix it especially given the period that the Home Hub 2 has been available.
As I indicated earlier in this thread i was on a fast connection with my Zyxel but I was getting line drops and a lot more noise and slow throughput (both wired & wireless). Eventually a BT Openreach Engineer came out and diagnosed a faulty circuit at the exchange. He also replaced the master socket. The line went to interleaved prior to the switch (so I can't say its the circuit that they swapped it to). We did get a power cut before hand and I think it was this and the line drops that fried my Zyxel. As soon as I plugged the Home hub in the noise dropped instantly and the throughput increased immediately to what I am now getting.
I therefore have no idea what is the cause of the errors. I suppose I am going to have to put up with them - I am still getting higher throughput speeds than BT's average on ADSL2+. BT have indicated that they don't think the errors are an issue and given the speeds I am getting I don't think I will get them to do anything further. Of course the hub hides the real upstream CRC errors. Given that you can't get much more than 1 meg upstream its not worth the hassle.
I have been thinking about buying a decent modem router as the diagnostic capability on the Home Hub 2 is limited (and it hides the real upstream errors). I am thinking of either a Billion 7300N or 7800N or a Linksys WAG 320N. The dual band capability of the latter has its attractions, but the very high approval ratings of both Billion's and their error handling also is attractive. I think that Zyxel have lost their way on the domestic market and their support was not the best when I was trying to eliminate potential causes of low speeds and high noise during the last couple of months.