I'm surprised that no one has mentioned the Peering transits used by the ISP especially when connecting to anything outside the uk, some of the smaller isp's seem to peer direct , where as some of the mass market ones don't this can make all the difference, especially the stability/consistency of the latency, the less fluctuation /jitter the better If this increase in latency is at peak times , then a change of isp may solve this peak time issue, but if the increase is due to a local issue capacity at your exchange then it's unlikely to change by a lot, unless the isp orders elevated from BTW All depends on how bad things are capacity wise