NOC24

Hi Everyone, I am in the process of starting a self-build in Northern Ireland. I have a site, which was passed 15+ years ago, and secured by the strip foundations and foundation blockwork being put in. We've decided to adjust the plans, with a change of house shape, which is currently with planning. We will have to remove the old foundations & start from scratch, which seemed like the best option for a number of reasons. Has anyone experience in understanding the removal process of old foundations? Will the entire strip foundations need dug out, then the area to be compacted again with soil, before being re-dug to the new plans? I know it is common in N.I for foundations to have been laid 10+ yrs ago to secure planning and subsequently updated, but i am struggling to understand exactly how it is done, to at least allow me an idea of costs and time associated with it Thank you