Manufacturers are under no legal obligation to supply parts for vehicles for a set period of time in UK law, although the majority of large manufacturers are signed up to a code of practice that states parts should be available while a vehicle is in production for a reasonable period afterwards. The Vauxhall Ampera was not sold in large numbers in the UK and went out of production in 2015, so this has no doubt contributed to the lack of parts. You could complain to Vauxhall UK, but your best bet may be to try automotive locksmiths or Vauxhall specialists in your area if you have not already done so.