1. A processor implemented method for detecting block errors in a video sequence having a plurality of frames, the frame being composed of a plurality of top fields and a plurality of bottom fields, comprising the steps of: a. detecting a scene change and determining a set of frames corresponding to a single scene; b. detecting motion between two consecutive top fields or between two consecutive bottom fields corresponding to the set of frames determined in step a, and determining one or more blocks in the top field or bottom field having motion, wherein each block is a matrix of predetermined size containing pixels; c. determining one or more candidate blocks within the top field or bottom field determined in step b, comprising the steps of: calculating a vertical gradient for the motion area of the current top field and current bottom field; thresholding the vertical gradient using a predefined threshold; processing the thresholded image using a morphological operation for getting regions corresponding to block errors; determining a corresponding horizontal edge and a corresponding vertical edge for each rectangular region; and creating one or more candidate blocks using the horizontal edge and the vertical edge; d. verifying the candidate blocks DCT statistics for determining the blocks with grid pattern block error, comprising the steps of: determining DCT statistics for the candidate blocks and for a predetermined size of neighbouring blocks by calculating a DC component, summation of AC coefficients, and summation of low frequency components; comparing the summation of AC coefficients of the candidate block with a predefined threshold; comparing the result of division of summation of low frequency components by summation of AC components of the candidate block with a predefined threshold; and setting the neighboring blocks high if summation of AC components of the neighboring block is greater than half of the summation of AC components of the candidate block and if the neighboring blocks are set high in a vertical, horizontal or diagonal line alignment then the candidate error block is rejected; e. verifying for block variation visibility, comprising the steps of: detecting if the block is present in the previous frame by calculating Sum of Absolute Difference of the block in a region of interest in previous frame, number of edges found in that region and structural similarity index for the structural similarity measure in the previous frame; calculating the mean of the block and deviation of each pixel value from the block mean; and calculating the transitions of the deviations; and f. validating the candidate block as an erroneous block if the transitions are greater than a predefined threshold.