Apologies if I'm being naive, but how does it take 3 architects a whole year to upgrade a family of websites to HTTPS? The BBC are way behind the times here, although the article alludes to issues with suppliers.
For each individual product, they need to figure out what modifications it needs to become HTTPS-enabled (lots of links and identifiers are hard-coded to HTTP, and third-party CDNs might not support HTTPS by default), and update their testing procedures to ensure that it remains HTTPS-compatible, before they can enable HTTPS. Given that this is the BBC (a publicly-funded entity), they also have to ensure that everything continues to be fully supported on browsers going back to IE6, Firefox 3, and Safari 3 - with partial support for some browsers older than them.
In my opinion, a year is doing pretty well.
They probably have more websites and hostnames than you'd realize, as well. Take a look at a site like https://dnsdumpster.com/ and search for bbc.co.uk