"Our car insurance automatically includes 100% offset of your car’s emissions for as long as you remain a customer"
www.greeninsurancecompany.co.uk
That's OK then - carte blanche to use the car. Is this credible?

"Our initial project is a new forest being planted at Helmburn farm in Ettrickbridge, Scottish Borders. Over 6,500 new trees will be planted there. Our money has enabled the project to go ahead and gives us exclusive rights to use the forest for offsetting CO2 emissions. Although a voluntary project the scheme will be subject to rigid audit to ensure that it delivers on its contractual commitments and that the new forest is being properly managed. We have teamed up with Forest Carbon www.forest-carbon.co.uk to oversee this. The forest will have full access rights and anyone is free to visit it. You may even hug the trees if you so wish."

Carbon offsetting is a smokescreen. It lets people avoid taking real action to tackle climate change by letting them think it's OK to fly / drive etc as much as they want. Offsetting should be a measure of last resort, after you have taken other steps to cut emissions.

There are big concerns about the credibility of many offsetting projects, with tree-planting being a top problem area.

For more information, see http://www.foe.co.uk/resource/briefing_notes/carbon_offsetting.pdf