on the doctrine of election which postulates that no party can accept and reject the same instrument and that "a person cannot say at one time that a transaction is valid and thereby obtain some advantage, to which he could only be entitled on the footing that it is valid, and then turn round and say it is void for the purpose of securing some other advantage"." 34. A party cannot be permitted to "blow hot and cold", "fast and loose" or "approbate and reprobate". Where one knowingly accepts the benefits of a contract or conveyance or an order, is estopped to deny the validity or binding effect on him of such contract or conveyance or order. This rule is applied to do equity, however, it must not be applied in a manner as to violate the principles of right and good conscience. (Vide Nagubai Ammal v. B. Shama Rao, reported in AIR 1956 SC 593, CIT v. V.MR.P. Firm Muar, reported in AIR 1965 SC 1216, Maharashtra SRTC v. Balwant Regular Motor Service, reported in AIR 1969 SC 329, .R. Deshpande v. Maruti Balaram Haibatti, reported in 1998 (6) SCC 507 = AIR 1998 SC 2979, Babu Ram v. Indra Pal Singh, reported in 1998 (6) SCC 358 = AIR 1998 SC 3021, NTPC Ltd. v. Reshmi Constructions, Builders & Contractors, reported in 2004 (2) SCC 663 = AIR 2004 SC 1330, Ramesh Chandra Sankla v. Vikram Cement and Pradeep Oil Corpn. v. MCD. reported in 2008 (14) SCC 58 = 2009 (1) SCC (L&S) 706 = AIR 2009 SC 713.