Petrol cars that meet the ULEZ standards are generally those registered with the DVLA after 2005, although cars that meet the standards have been available since 2001
Diesel cars that meet the standards are generally those registered with the DVLA after September 2015

Information from Transport For London

Check this car on the TFL website before purchasing: https://tfl.gov.uk/modes/driving/check-your-vehicle/

To save timely negotiation all our cars are heavily discounted upfront and offered nearer cost price, saving customers up to £2000 when compared to our competition. This ensures we are treating every customer the same. This fee is a compulsory fee and applies to all customers.

Variable admin fee is charged as listed below:

Retail customers pay £199.
Repeat customers purchasing a 2nd car within 12 months of the original invoice date £0.
Retail customers arranging finance using brokers outside of our immediate panel of lenders £399.
Trade customers making a purchase as the motor trade £499.
Export customers including Northern Ireland and the Republic of Ireland £499.