As an advanced response / pursuit driver myself, I may be able to shed some light on the criteria we use. On red ring speed limits we (just like the normal panda bobbies) are allowed the speed limit + 20mph on top ie. if it was a 40mph we CAN if its safe to do so do 60 mph. The only difference is on nationals where advance drivers can use speed (if safe to do so) above & beyond the +20mph.
In the event of a pursuit the are MORE rules to follow & only advanced drivers can pursue (Local beat bobbies can initially pursue until such time as advanced drivers join them OR the speed goes over their 20mph exemption. Then if an advanced car gets behind the target they HAVE to give all the pursuit criteria to the control room boss. ie. speed, road conditions, speed limit, time of day, any pedestrians, schools in the area, etc. etc.etc. and have to relate all that whilst driving giving none stop commentary. The control room boss has over-riding authority on whether the pursuit continues or not, BUT the onus is on the advanced driver to (for want of a better word) paint a picture of the scene & circs. If the pursuit is authorised then the running commentary has to continue all through and the driver can use speed (if safe to do do) in excess of the limits. If either the control room boss thinks that the pursuit is too dangerous they can call it off, just as the officer on the ground can. If the officer doesn't give good commentary, again its called off. If the get away car does something outrageously, and we aren't allowed to follow (wrong way along the motorway), again its called off.
I'm not familiar with the case discussed, so don't know the circs, but I believe that it was his own force that reported him to the CPS who took the case up??? 108mph in a 40 seems a bit
to me really, but again full circs are not known.
At the end of the day it does boil down to the drivers training and I know there are good ones and bad. Black box technology is king now so if the wheel falls off, and something serious happens we can & should, (and have been) be held to account.