I am trying to download a temporary insurance cover note but my computer keeps saying it contains a virus so I am unable

If your absolutely sure it doesn't, then turn off your anti-virus temporarily to download. But, if I were you, I would double check the file. Either by scanning it with another AV or sending the file to one of those online scanners like virustotal.com. Hopefully the file is a zip or rar file that will not infect you unless you open it. So don't open it until you check it online.