Agree - GDL is more than acceptable and there is no point doing a second degree. Also, he would still have the option to be a solicitor when he comes to choosing between the LPC/BVA (that said, he would have missed the boat for applying for training contracts as a solicitor to start as soon as he finished law school).
Is he at Oxbridge now? If not, is the uni one of the older unis rated in the top 10 or so (LSE, Kings, UCL, Bristol, Durham)? If yes to one of those, is he online for a good first (NOT a 2:1)?
Honestly, if no to any of the above, the bar is a VERY hard ask, and unlikely to be successful.
He also needs to bear in mind that the early years of being a barrister, even if you go for one of the better chambers doing more commercial work (not criminal law etc - think chambers like Matrix or some of the well known tax and chancery chambers) AND is successful (honestly, so much competition), are very tough financially - many change to being a solicitor simply because they need a regular monthly income. Another thing with solicitors is that you get funding for the two years of law school if you get a training contract early enough. So if he were in his final year of his first degree, he might JUST be in time to apply for a TC this year and then get funding for law school. Akthough not without work experience and again, he'd need to be online for a first really.
Re politics, I am a lawyer (did you guess?!) but have a couple of close friends in politics. Is he already well involved in a political party? Has he been doing a lot of student politics and work experience? I am afraid the days of the route of barrister to politian automatically have long gone. Politics requires work experience etc these days, just like everything else.
I hate to be so negative (and your friend's DS might have all the above or more), but you need to bear in mind that there are literally 1000s of young people who DO have all of the right grades and experience etc, so without them, its an uphill battle.