Is there any way to disable or remove the [ T ] Tesco navigation button on a Hudl?
Well that took quite a bit of work.  In the end I was able to get the custom firmware for the Hudl mentioned on the MoDaCo forum.  After that the difficulty was getting the USB Drivers up and running to get the Hudl happy as an MTP device.  I think this is how it went...

Enable Developer Settings &amp; USB Debugging - This Hudl is an Android 4.2.2 device so you got to Settings > About Device scroll down to Build Number and then tap it 7 times.  After that you will find that you can go to Settings > Developer options then enable USB Debugging.  

USB Drivers - Honestly I don't know what I did to finally get this working.  Even with the Android Development Kit installed the drivers did not load correctly.  Some scrabbling around took me to the AndroidCentral Forums from which I downloaded a MotoHelper Driver, extracted the files from that install executable and then installed the 64 bit driver version under \MotoHelper_2.1.32_Driver_5.4.0\$TEMP\ (this took me two attempts).  After failing to get an Unknown Device to install as a composite mtp devices, I tried replacing some of the other ones that came up; a Hudl and an MTP device.  That did not work so I unplugged the device, plugged it back in.  Eventually a second Hudl device appeard and this I could choose to be a Composite MTP which then let adb devices -l see the thing.  

Backing-up the old and installing the new SystemUI.apk - This turned out to be the easy bit.  Follow the instructions from the MoDaCo forum post.  Navigate to wherever you have the new .apk in a console and then:

adb pull /system/app/SystemUI.apk SystemUI.mybackup.apk
adb push SystemUI.apk /sdcard/SystemUI.apk
adb shell
su
stop
mount -o remount,rw /system
cp /sdcard/SystemUI.apk /system/app/SystemUI.apk
chmod 644 /system/app/SystemUI.apk
reboot


I am very grateful to PaulOBrien for getting the modified ROM setup and providing the instructions that got me most of the way.