Unforeseen cost increases

We operate an NEC 3 Term Service Short Contract for a maintenance contract. Over the past 12 months the availability of materials has become limited and some of the materials that we provide as part of this service delivery have gone up in excess of 400% from this time last year. We are based in Northern Ireland.

There is an inflationary uplift but this basic uplift is not sufficient to deal with these cost rises

Timber, steel, horticulture materials and so on are all seeing rises in excess of 200%

What would be our approach with the client as we believe that we should have made a best guess that our rates in our schedule of additional rates would cover annual prices increases, but there’s no way a competent contractor would have even Come close to factoring in such price rises.

How do we approach our client, and what clause etc should we be using to ensure the extra over cost increases is. It absorbed by us as a contractor as this would out us out of business in no time at all.