With the exception of bodies such as Learn Direct and the OU, all distance learning courses in the UK are provided by private companies. While a few of them pay to have their courses listed in online directories, most of them recognise that such advertising won't get them any more attention than simply ensuring that their website is quickly found by Google. So there's no useful directory available online.
LearnDirect and the OU are generally far cheaper than private firms (because they don't need to make a profit from their activities). Their qualifications are also generally more widely recognised. However, if they don't offer what you want, all I can suggest is Googling for suitable courses and then (when you've found something which looks interesting), Googling again for the name of the college/firm, together with the word 'review'. (That should flag up any warning messages about 'dodgy' institutions).
If you're thinking of a particular career path, you can find out what qualifications are recognised for that career by looking through the job profiles here:
https://nextstep.dire...es/Pages/default.aspx
Chris