The Metrodecker is just an Olympus with an Optare chassis. The Olympus was a double deck Esteem, which itself was just a full body update of the Myllennium. No prizes for guessing when the Myllennium hit the market.
Neither the Myllennium, Olympus or Esteem were Optare products, they were East Lancs products, the first of which was long out of production by the time Optare brought them out and the later two were produced by both Darwen and Optare who bought East Lancs and Darwen out respectively.
The Olympus was an updated version of the Scania based Omnidekka and all of the other Myllennium double deck bodies. The Omnidekka was literally a Myllennium with a Scania front and back end that had a few tweaks to be adapted for a Scania chassis.
Originally Optare planned to build their own chassis for the Olympus but that never happened and they went down the Rapta road, which eventually ended in the Metrodecker which essentially was a new product, based on their experiences with the Rapta and the Olympus Optare chassis prototypes and a fair few new ideas.
It would have been good if East Lancs survived to tell the truth as they would be picking up the kind of business that MCV are now. When Optare took them over they before too long closed down the old EL factory and laid off a good few of the staff and abandoned any EL products.
The Olympus was generally a flop though. It was supposed to replace the Omnidekka, but ironically the Omnidekka outlasted it and outsold it and this is despite the fact that after the Olympus was released, Darwen and Optare didn't do a single thing to try and sell any more Omnidekkas and only really entertained building them for existing customers, which ultimately cost them orders.
By the way, this is the Optare chassis'd Olympus
https://www.flickr.com/photos/146674753@N06/26211592347/in/photolist-FWegcZ-XQ1gQV-YbToQa