1. A method for estimating motion in a sequence of video images comprising: storing a plurality of fields of a sequence of video images, for each of a plurality of blocks of pixels in each field; and testing, for each block of the plurality of blocks, a plurality of candidate motion vectors to determine which candidate motion vector gives the best fit in determining the motion in the image between adjacent fields for that block, wherein the testing comprises determining the amount of motion blur present in a portion of the image including that block, and modifying the testing of candidate motion vectors in dependence on the thus determined motion blur, by applying a weighting factor to each candidate motion vector in dependence on the determined motion blur, the weighting factor for each candidate motion vector being dependent on the direction of the candidate motion vector relative to the direction of the motion blur, wherein candidate motion vectors with vector components which are inconsistent with the direction of the determined motion blur are penalised by the weighting factor for that candidate motion vector.