A regular process of tying and trimming new growth on espaliered fruit trees is essential to manage size and form.  Shorten vigorous upright growth that interferes with the desired form.  When tying down horizontal branches, keep at least the end 20-30cm untied and growing upright, as tying the entire branch down will stop growth altogether (which should be done when the branch reaches the desired width). Regular clipping through Summer is much more effective than an annual Winter prune.