Adopting the philosophy of reuse, recycle or rethink, the best option is to find an alternative use for the old platforms before expending vast amounts of energy in moving, dismantling and melting them down.
Any fisherman or scuba diver (including myself) will tell you that marine life congregates around even the smallest irregularity on the sea bed - and large wrecks in particular.
Professor Bellamy's plan finds a new use for these structures which saves money, saves energy, returns iron to the sea and provides a mechanism for preserving fish stocks, which are nearing the point of irreversible decline.
The oil companies (and the Government) could use some of the money saved to set up a hatchery programme to boost stocks of juvenile fish on the new reefs. These could be maintained either directly by the fishing industry or by switching subsides from the fishermen to the hatcheries.
This solution is not merely "using the sea as a dumping ground".