i use a hour guard
the other day i worked 14 hours, and had 11 hours rest
but the hourguard took it as i had a nine hour rest
So i wondered if i work 15 hours MUST i class it as a 9 hour rest too
your minimum daily rest should be 11 hours mate.
however you can reduce it to 9 hours on 3 occasions through the week BUT you must compensate for it before the end of the following week.
for example…if you reduce your rest to 9 hours on one daily rest,but the next night you have a 13 hour rest you have paid back the rest you borrowed 
By definition if you work a 14 hour shift the most rest you can possibly have is 10 hours, but you can take 9 if you want. Doesn’t matter if after a 14 hour shift you rest for 11, 12, 13 or more hours it will only be a 10 hour rest and will be one of your 3 allowed reduced daily rest periods in a week.
The whole rules are built around how much rest you need in a 24 hour period, beginning when you resume work after a daily or weekly rest period, and this is usually 11 hours which can be reduced down to 9 hours 3 times a week. (I’m ignoring split shifts for now as that would just complicate things.)
This means that if you start work at say 07:00 Monday to fit an 11 hour break in before the 24 hour period ends at 07:00 Tuesday you would need to be finished no later than 20:00 on Monday evening, 13 hours worked 07:00 - 20:00 + 11 hours rest = 24. If you go past 20:00, even by just one minute you can no longer take an 11 hour break by 07:00 Tuesday so you have reduced your rest period.
If you work 15 hours from 07:00 Monday that takes you to 21:00 Monday evening and only leave 10 hours before 07:00 on Tuesday so that would be a 10 hour rest period. You can resume work after 9 hours at 06:00 Tuesday. It doesn’t matter if you actually take more than 10 hours before starting work on the Tuesday, you might not start until 09:00, and that is 12 hours after finishing at 21:00 on the Tuesday, only the 10 hours up to 07:00 fall within the 24 hour period so that is a reduced rest.
The easiest way to remember it is that if you work more than 13 hours after starting work, even by one minute, you have by default used one of your allowed reduced rest periods, no matter how much rest you actually take.
Bet your glad I didn’t make things complicated with the split shift system. 
Sorry, that was rude of me, I should have said welcome to TruckNet UK Andy.
i was also going to say welcome to trucknet andy but as you joined in 2003 i thought it would be a bit silly.
also i forgot to add that my above figures are correct but they are made on the assumption that they would be for a 24 hour period.
your question has been changed otherwise i would have said go by the hourguard mate
i was saying welcome because it was his first post even though he joined in Nov. 2003.
I see you have changed your question since we answered it Andy but my answer still holds true in your case. Because you had worked more than 13 hours and therefore it was impossible to fit an 11 hour break into the 24 hour period the Hours Guard was correct in taking one of your available reduced rests. You say you took 11 hours rest but only 10 of those hours fell into the 24 hour period.