Put simply, no.
When the Energy Performance Certificate is issued it will come with an Recommendations Report. This report will include some recommendations to help you save energy, reduce your energy costs and reduce your CO2 emissions. It will also give you an idea of the typical cost of making these improvements and the reduction in emissions that is likely to be associated with each improvement.
However, these improvements are not mandatory and it is up to you to decide whether or not you want to make them. You will want to consider how quickly the savings will pay for the improvements and what impact the changes will have on your property. In some cases you may not even be permitted to carry out the necessary works for example, you may live in a conversation area and the changes may not be permitted.
In the future some buildings with very low ratings may have to have improvements carried out to improve their overall rating. Even so, it will be up to the owners to decide which improvements they wish to make. This is already the case in Scotland where some buildings now require a Section 63 Action Plan.