Clipped Box has been popular in British gardens for centuries-but it is under attack. Box blight has been with us for some years now. The best defence is to keep the plants healthy and vigorous. Foliar feed seems to work especially well. Also, be careful- we have had reports that some inexpensive Sarcococca in the large outlets have been found to have something that looks suspiciously like Box blight. Sarcococca is the same family as Box so it could well be. Do not import trouble.
Then there is the caterpillar. Box moth is very active in this area and can devastate hedges and topiary extremely rapidly. Be vigilant and take action immediately. (How you tackle the critters is up to you. We are not allowed to advise) If you do suffer damage, again, feeding is important. The plants will try to regenerate and it is essential that they have sufficient nutrients to do so.
If you decide to give up and replant, there are alternatives. Ilex crenata is an option but it is slow growing and will not tolerate wet conditions. A good choice though for a parterre. Increasingly popular is Euonymus Green Spire, it looks the part and is strong and tough and not excessively vigorous. We now keep it on the nursery as a stock item. At present available in 1L, 2L, 3L pots as well as a few specimen plants.
The images below
The first two images are showing the Euonymus Green Spire;
The third one is Box.