I did a PGCE when I graduated from my BA. It took a year & there is a bursary to help cover costs (between 6,000 and 9,000 depending on level and subject). After that, I taught for two years. It was only at this point that I went back to university to do higher study ( Master's and now PhD). I think having time out in the "real" world helped me in a number of ways, Mainly : it has made me a lot more balanced about doing a PhD, and more secure in terms of knowing that I can always earn money; also, I learnt some amazing (invaluable) people skills and work habits.

You don't really explain why you want to do a PhD -- do you actually want to be a teacher or is it just for the experience of doing something different before you plunge back into the madness of academia My advice would be that, if you want a career as a teacher, do the PhD then a PGCE, but if you want a career as an academic do the PGCE first.