Hi Paul,
Since you are expecting high amount of traffic from the very beginning and you also need root access, you could start off with a VPS or a Semi Dedicated Server and perhaps upgrade to a dedicated server gradually as the traffic grows further.
As far as control panel is concerned, you can choose either cPanel/WHM or Plesk with VPS/Semi Dedicated Server depending upon your preference. Both of the feature sets are pretty much comparable, and both are reasonably fast, secure, and reliable.
You can check Linux VPS Hosting plans at
VPS Hosting - Virtuozzo WHM Cpanel VPS Hosting- UK Virtual Private Servers and Semi Dedicated Servers at
Semi Dedicated Servers UK | Linux - Windows UK Server Hosting