The most striking common problem of mature industrial economies is obsolescence. Physical obsolescence is marked by slum housing, old factories and industrial plant, the mixing of land uses, traffic congestion and the overstraining of ageing service facilities; while economic obsolescence is based upon a degree of concentration into activities that no longer have a major potential for growth. There is the 'internal structure' of the regional economy. Regions are capable of an element of self-sustained growth, based upon the internal structure of linkages between various industries or services, and between them and the rest of the country. The roots of intra-regional planning in Britain are in the slums. The housing situation dominated the first round of plans initiated by the Government during and immediately after the second world war. The Board of Trade has considerable experience of industrial relocation and development through its statutory responsibilities for controlling Industrial Development Certificates.