Error correction coding based on soft-input decoding can significantly improve the reliability of non-volatile flash memories. This work proposes a soft-input decoder for generalised concatenated (GC) codes. GC codes are well suited for error correction in flash memories for high reliability data storage. The authors propose GC codes constructed from inner extended binary Bose–Chaudhuri–Hocquenghem (BCH) codes and outer Reed–Solomon (RS) codes. The extended BCH codes enable an efficient hard-input decoding. Furthermore, a low-complexity soft-input decoding method is proposed. This bit-flipping decoder uses a fixed number of test patterns and an algebraic decoder for soft-decoding. An acceptance criterion for the final candidate codeword is proposed. Combined with error and erasure decoding of the outer RS codes, this acceptance criterion can improve the decoding performance and reduce the decoding complexity. The presented simulation results show that the proposed bit-flipping decoder in combination with outer error and erasure decoding can outperform maximum-likelihood decoding of the inner codes.