Whether or not ring final circuits result in a saving of copper is totally dependent upon the layout of the sockets - and the saving will often be minimal or non-existant. Indeed, in some situations, a ring final circuit can use more copper.The thing is the reason for the introduction of the ring circuit aka the shortage of copper, is as valid today as it was 70 years ago. Put simply long term there is insufficient copper in the world to go around. Consequently any move to radial circuits in a country that already has ring circuits is complete madness from a strategic viewpoint and should be resisted.
For a start, one can cut any 2.5m² ring final circuit into two 20A/25A radials, without changing the amount of cable/copper being used, and actually with a consdierable increase in amount of power available (40-50A, rather than 32A).
If one really feels the need to maintain a 32A total capacity for each circuit, one has to move to larger (usually 4mm²) cable. However, with some layouts of sockets (the extreme case being if they are all 'in a straight line'), the total cable length for a ring will be roughly double that required for a radial. In those situations, the radial will actually use less copper, since the total copper CSA of 4mm² cable is 9.5mm² (4+4+1.5), whereas the total CSA of 2.5m² cable of 6.5mm² (2.5+2.5+1.5) is considerably more than half that of 4mm² cable.
To take an example, with sockets in a straight line and the furthest 10m from the CU, the total amount of copper for a 2.5mm² ring final would be 130,000mm³ (about 1162g) whereas that for a 4mm² radial would be 95,000mm³ (about 849g).
With careful circuit design, one can often use less copper with radial circuits than with ring ones.
Kind Regards, John