Does the nonbreaching party to a contract has a duty take all reasonable steps to reduce his damage from breach under English law?

Yes, the non-breaching party has a duty to take all reasonable steps to reduce their damages from breach of contract under English law. This is known as the duty of mitigation. The non-breaching party must take all reasonable steps to mitigate their losses, such as seeking alternative sources of supply, or seeking to recover their losses from a third party.