In this question M cannot sue P as per ICAI shouldnt answer be M can sue P?
No M cannot sue P ( it was Without concern of P) also M reduced the rate of interest. Because of this P is discharged.
But aren't the variation in terms beneficial for P?
Good question and discussion above. It's a material / substantial variation, even when it seems beneficial because insolvency could have been avoided through n ways and hence, consulting P was important. So, M can't sue P. Relevant provision is: Variation which is not substantial or material or which is beneficial to the surety will not discharge him of his liability. But here, it is material / substantial. Happy studying!