Now I`m not a lawyer(Ruth?)but it would be handy if we new the law on this

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Sparkin, I'm not a lawyer either, yet! And I haven't got time at the moment to look this up. However, as has been said, practices that restrict consumer choice are frowned upon under EU law. But the practicalities are, you'd never go to court over something like this because of the cost.
Chris large, this thread will be useful as proof of people's positive experience of warranty claims after having a non-Ducati service. If you can show that most people have had no trouble as long as their service met the criteria, you ought to be able to insist on equal treatment.