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The question is one of organisation. Nobody with any sense is going to be the organiser because of liability, never mind CTT's view. However, the time and place of a TT is a known-distance test track which has already been risk assessed, so it will be no surprise if one or more people choose that for a training session, especially now that they know they won't be breaching etiquette by doing so during an actual organised TT.
You say that, I've already received directive from CTT that a very dim view will be held on people trying to do so (I'm the club event secretary for Midland DC, couple of clubs in Midland have already tried to organise unofficial TTs - a member of the public threatened to go to the police because of what Banbury Star CC were planning to do).