Cars don’t usually qualify for the annual investment allowance.
For several years though it has been possible to claim a 100% first year allowance (FYA) on low CO2 emission cars.
This tax break was due to end on 31 March 2015 but on 17 February 2015 new legislation came into force to extend the 100% FYA until 31 March 2018.
The downside is that the new law also lowers the CO2 emissions limit from 95g/km to 75g/km for cars bought on or after 1 April 2015.
A list of low emission cars.