Not all that long ago, the Office for National Statistics unveiled their new website which, in my view, is significantly better than the old one (screenshot of the new site below). There have been some teething problems but I just wanted to highlight some of the interactive data features.
There's a box to the right of the home page which says 'Interactive Content' and if you click on it you will be taken to a page full of more interesting visualisations of ONS data. There's a map and data visualisation using unemployment benefit claimants plus lots more.
On the population page, you can also see up to date snapshots for the UK, including the up to date total population (currently estimated to be 62.3 million). The site is not yet perfect but is definitely worth a closer look.