df <- data.frame(Postcode=c("EC3M 7HA", "EC2P 2EJ"),
                 Tip=c("<a href='http://www.lloyds.com'>Lloyd's</a>", 
                 "<a href='http://www.guildhall.cityoflondon.gov.uk/'>Guildhall</a>"))
M2 <- gvisMap(df, "Postcode", "Tip",
              options=list(showTip=TRUE, mapType='normal',
              enableScrollWheel=TRUE, width=500, height=300))
plot(M2)