Selling CDs not against the law, but the copying of CDs for own personal use on iPods and hard drives technically is, following a change to the 2015/2014 legislation which allowed this. A music industry group undertook a judge led judicial review which appealed the legislation.
But I do think these firms offering this service are doing no other than what individuals can do on iTunes and other ripping software e.g. Db poweramp. As I've understood from some of them, the rights department of the government have no intention to take any action against these firms. It could be a problem with the industry associations doing so, but I suspect they turn a blind eye, as it's small fry to the overall issue of people doing it anyway. Last I heard they were trying to get a tax on the sale of hard drives to make up for the stated £58 million losses and I suspect the motivation to allow some form of change of legislation was to make it easier for this to happen, not to try and legally penalise cd owners, iTunes, and all the computer manufacturers which make cd copying something that is so widespread, any combating of the industry to deal with it would not only be cost prohibitive, but would not be upheld in the courts on balance.