2006 Vauxhall Zafira engine management

Warning light(car with spanner) displayed whilst driving.Checked handbook and switched off engine as recommended. When restarted warning light reappeared after about 5 mins. took car to local dealer who completed diagnostics.Claimed problem related to 'timing variator kit' as as part of repair vehicle would need a new timing belt. Quoted £1k for repairs!!!! Car done 25K miles and is only 5 months outside its 3 year warranty. Is it reasonable to expect such a major problem to occur under these conditions? The dealer has subsequently reduced the repair quote by £300 based on customer loyalty and a contribution from Vauxhall. Any thoughts on how i can pursue this further?