It was created using a CMS called DotNetNuke.
You can tell it was created by some kind of automated tool and not hand-written because of the amount of nonsense in the code (right-click and View Source to see what I mean), including such gems as
id="dnn_ctr453_Links_lstLinks_linkHyp_1". And therein lies your clue as to which CMS it was, because a huge number of labels and functions are prefixed with "dnn_", and a quick Google then gives the game away!
It is a CSS-based design that seems to be doing a reasonable job of semantic code, but it is a horrendously bloated page, with lots of redundant class names and redundant nested elements. By all means take design inspiration from the site if you like the look of it, but in terms of the code base, you need to take it with a huge pinch of salt.
I'm really intrigued by the link that says "Download the Divorce UK app from iTunes" ... just how often do they think people are going to get divorced that the need an app for it? :lol: