Inspired by Weavers suggestion of Germany buying Chieftain as a heavy tank, how about the UK buying Leopards, in particular Leopard I, as a medium tank.
Back story, While fine for BAOR exercises in Norway, experience in the Falklands and later in the former Yugoslavia, demonstrates the need for a lighter, more mobile tank than Chieftain or Challenger to support Marine, Airborne / Airmobile and light infantry forces, a new medium tank. There is a precedent for this, I have read that the Germans placed Leo 2s in reserve while retaining Leo 1s in some units due to their lower weights based on experience in the Balkans.
It could be that the desired vehicle is actually the M-8 or the Vickers Mk5 derivative, but the Leopards are readily available and much cheaper.
Weaver prompted this latest but the idea is much older, an idea I had years ago, involving the re-roling of the Household Cavalry Regiments to better support and supply significantly more combat power to amphibious and rapid deployments.