Is this true? Yes and no.

Yes, if he is blue at moment as on moving to France, since 420 tier points exceeds amount required for Euro Silver (400), he is promoted to silver and points reset to zero (even if there are more points than required for silver). In this example, 20 tier points would be wasted on the reset. New membership year starts at this point.

No, however, if he is already UK silver, 420 tier points will stay on his account and membership year will remain the same. SYD flight will then add to existing points on way to Euro Gold at 800 tiers points.