Kev W

Hi, Just new here and looking for lots of help and guidance. Planning to extend a bungalow to the south, flat roof, giving extra 2 bedrooms, kitchen/diner and utility room. Had to go for neighbour consultation under PD Large extension which passed without issue. Have now submitted Building Notice and planning the foundations. This is my biggest concern and have been advised to dig out to solid ground (600 wide) and then call inspection visit. The patio area being built on currently houses a large conservatory but there is a 5' retaining wall about a metre from the proposed footings where the lower level has been previously excavated (See photos) Is it likely that I will have to go down below the ground level beyond the retaining wall or will a structural engineer have to be called in to advise? Cheers, K