We were at one of the MOT Seminar's last night and there was a representative from Siemens there who was asked to explain what had happened.
He said that there was an issue with the system running slow as there seemed to be a lot of garages that had logged on for the first time this year (!) and as result were reading all the messages that had been sat waiting since before Xmas. This resulted in whole thing going slow which resulted in 900 NTs have problems logging vehicles for test (not sites, just individual testers).
What compounded the problem is that BT had a major trunk failure in Durham (I think) where one of the call centres are located. This meant that a large number of calls just disappeared into a black hole. He also said that they have now opened another call centre (in Glasgow) which is currently have staff trained so can't answer as many calls as the other site. The phone system is to load balance between the two sites, but if a call got routed to Glasgow and could not be answered (due to few numbers of staff) the call was automatically routed back to Durham and hence disappeared due to the trunk failure.
This only affected a couple of the stations that attended the seminar last night and it was stated that anyone after compensation would need to write in, including as much supporting evidence as possible (diary bookings, logs, etc) and each case will be looked into.
This has been classed as a major incident and a full investigation will be done to see what happened, why it happened and how can it be prevented. He did say that a new release of the software is waiting to go out to help prevent the system from slowing down too much under such a situation.
Some interesting statistics were that they have now got over 15,000 stations online and there is in excess of 97,000 MOTs being logged everyday.
Also, there were 7 MOTs performed on Xmas Day and there was 1 call to the Help Desk that day.....though that may have been someone just checking to see if there was someone in to answer the phone!
Hope this helps.
P.S. The above is how I understood what happened from what I heard last night.