OP, if you're still considering it, here is my view.
I joined the Leeds office of a multi office commercial firm when I qualified. I have worked in Leeds for 12+ years, from my "young free and single" days, to now having 3 children. I am in a contentious sector, and agree that it is very unpredictable, can be long hours but rewarding on lots of levels. I do found it intellectually challenging.
I managed to work part time after I went back after maternity leave, and generally left the office at a reasonable time on all but one of my days, but I was at my desk for 7.15/7.30 each morning (never saw the children awake in a morning on my work days) and had one night where I stayed until about 10pm each week (as my H could collect the children and I caught up at work). I was employed for 21 hours - but probably did 35-40. I was however sidelined as soon as I went part time, I wasn't promoted for 7 years (although I was handling big cases). Apparently if you work 3 days, even if you're doing the same % of extra hours, BD events etc as your colleagues, you have clients calling you on the other days, you do telephone Court hearings from home with 2 toddlers shut in the lounge in front of the TV with a packet of chocolate buttons to keep them quiet for 10 mins you're "not committed". I think if you have any vision of making it to senior associate / director / partner, you will need to work full time.
I disagree with some of the others that your academics won't get you into commercial firm (I did have some involvement with recruitment). I think my firm anyway was a lot more savvy with applicants than just going on grades or which uni you went to. Don't get me wrong, I am sure that there are still firms out there who are quite rigid with their recruitment requirements, but I think my experience is that people are looking for something "extra". They want someone who is down to earth, able to relate to clients, business-minded. Certainly when I first started getting involved with recruitment I was told to put anyone with a 1st in the bin (Yorkshire partner said he wanted people who had experienced life at uni rather than sat in the library for 3 years!).
Having said that, its not a career I would have chosen with hindsight unless you have a very good support network. As everyone else has said, it is very difficult to get a foot in the door and in many ways, it is still who you know and not what you know. I've been a mentor at Leeds Met to students on the LPC and there are only a handful of training contracts to go round. Most LPC graduates are now applying for paralegal positions (very poorly paid) just to be doing something related.
Even when you qualify, it is also not very well paid, compared to equivalent professions, and very stressful. The implications of missing a deadline for instance are massive and I don't think you get that in many other professions.
I'm not saying don't do it, but do your research, try to get some voluntary experience if you can't get a placement, pull any strings you possibly can to get any access to a law firm that you can and go into the decision with your eyes open. Good luck!