The business will sell UK-sourced new cars supplied by BCH at fleet prices.
Online quotations are available for vehicle insurance and policies can be issued via email.
It is expected that thousands of sales will be generated in the first year, with deliveries being made to customers' homes by BCH.
Discounts range from 3% on a BMW 318i up to 25% on a Fiat Marea. Significant savings are also available on a range of Renault models.
Peter O'Connor, managing director of the £40m five-dealership group, has been appointed deputy chairman to give full-time focus to online activities.
The website (www.ecomocars.co.uk) incorporates price and specification data from Carspecs.com, together with a comprehensive selection of finance packages constructed in collaboration with accountants Grant Thornton.
There is also an editorial section with car reviews and spy-shot photographs.