The difference is that connecting to an VPS outside of UK legislation is a process which encompasses pretty much everything, from email to webbrowsing to whatever. The traffic is HTTPS encrypted and looks like any other legitimate traffic. What the VPS does afterwards is invisible to the UK Government. If the UK doesn't want to put up a great Firewall that makes China blush, there is no way to prevent this, and legislation that cannot be enforced is dead law.

Also, this would be very disruptive for any business that isn't totally local, which is an pretty good incentive to not do this if they dont want to cripple their economy.