I wondered about that between Weston and Highbridge. According to my phone GPS, it got to about 106mph before having to slow down for Highbridge[pedantic mode]
They are timed at 110mph on lines that do have a line speed of 110mph (or more), and yes, that includes part of the main line between Bristol Temple Meads and Penzance. Although I don’t know how fast drivers are permitted to drive them at.
For the record:
- South Liberty (near Parson Street station) to Uphill Junction (near Weston-super-Mare) is all 100mph.
- Uphill Junction to Huntspill (near Highbridge & Burnham station) is all 110mph.
- Huntspill to Cowley Bridge Junction (near Exeter St. Davids station) is all 100mph.