Why is it only the US & Britain who want to hold Iran back from nuclear power?

If you bring Israel into the mix I guess we would be halfway to a reasonably accurate guess. The Yanks and Brits are dead scared of a preemptive military strike on the reactor by the Israeli Air Force who, it is reliably reported, have already a done deal with with the Saudis to overfly their airspace. If this happened it is reasonable to forecast that the West's oil supply chain would receive serious interruption. Also,should such an air strike take place following the installation of nuclear fuel rods it's reasonable to forecast a mive radio active fall out in the area which would probably affect both Russia and her neighbouring states and Pakistan.