Organize an appropriate group of experts to collect all relevant information about these articles in order to provide a complete todays cost of purchase (if any), transport, repair, building of display areas, and all ongoing costs of maintenance and upkeep including security and safety and salaries of custodians, and costs of packaging and transport to Greece and all converted to todays costs. This figure should be presented to Greece as the total cost to Britain for preserving these artefacts that were ignored by Greece until saved by Lord Elgin. Only when Greece makes this payment (which would be increased by ongoing costs) would these artefacts be returned.

I have no idea how much this would be, but believe a very (very) large amount.