As promised, I have some information with regard to the problems you are experiencing with your clematis. It would appear from your description that there are two pests which could be responsible for damaging the flower buds; earwigs, as you mention, or caterpillars of the angle shades moth. For a definitive identification of the pest, you may have to venture into the garden after dark where you should catch the culprit red-handed, but below are some pointers on how to control both pests.
Caterpillars of the Angle Shades Moth – coloured green to brown with a light band along their back and V-shaped markings down each side, these caterpillars are soft and plump in appearance. The adult moths are active from May to October in the garden and lay clusters of 50-100 eggs on the leaves. The caterpillars hatch and feed on leaves, buds and flowers before dropping to the soil and pupating. There are normally two generations of adults each year, but the life cycle can continue all year in heated greenhouses. Controlling the caterpillars is the best form of prevention; inspect the plant regularly, destroy batches of eggs and remove caterpillars, check the soil around the base of the plant (or in the pot) for pupae and spray the caterpillars with a contact insecticide such as derris (available from our website product code GPC-680).
Earwigs – females overwinter in soil and lay 50-100 eggs which hatch in March. The adult earwig will feed the young until they mature and disperse in early summer, when they live in the flowers and foliage of ornamental garden plants – including clematis – and feed at night on petals, leaves and buds. Good garden hygiene, such as clearing rubbish and plant debris, will reduce the sites suitable for the female to overwinter, and laying cardboard on the soil surface will attract earwigs which can then be removed. You can also fill an upturned flower pot with straw and place it on top of a cane or stake to trap earwigs - but chemically, derris is not really effective. Ideally, identifying the pest will help you implement more effective control measures but hopefully this information is of some help. You may wish to post your enquiry on our Online Gardening Forum, accessible through our main website (see address above) or directly through this link weblog - you may find that some of the many regular visitors have experienced similar difficulties and can reply to your post, offering further help and advice!
Many thanks once again for your enquiry and we hope to be of service to you in the future.