Both models are adorned with Seat’s E Ecomotive moniker, designed to identify the lowest CO2 emissions in each of the Spanish manufacturer’s range.
From 1 January 2011, drivers of the Ibiza E Ecomotive and Leon E Ecomotive will not have to pay the £12 charge, which itself is up from £10 for 2011.
This is because the criteria for exemption has changed from all alternatively fuelled vehicles to those with official CO2 emissions figures below 100g/km.
In the case of the Ibiza E Ecomotive, CO2 emissions are just 92g/km from the 1.2-litre diesel engine, while the Leon E Ecomotive delivers CO2 emissions of 99g/km from its 1.6-litre diesel unit.
Director of SEAT UK Peter Wyhinny said "Obviously we’re very pleased that the Mayor of London has modified the Congestion Charge exemption to become a technology-neutral,CO2-based system."
Owners of the cars will need to pay a single fee of £10 to drive into the capital for a year free of charge.
Both models also qualify for them bottom rate of Vehicle Exercise Duty, meaning they will not need to pay towards the road tax.
This makes the Seat Ibiza and Seat Leon E Ecomotive versions two of the cheapest non-alt fuel vehicles to run in the UK.
Seat says the Ibiza E Ecomotive, the most frugal of the two, is capable of travelling 800 miles on just £60 of fuel for three-door, five-door and estate models.
The Seat Ibiza E Ecomotive and Seat Leon E Ecomotive join models such as the Vauxhall Corsa ecoFLEX, Ford Focus Econetic and Citroen C3 Airdream+ as some of the latest cars eligible for free entry into London.