if going to Southwark park go early-it gets very busy as one of the few free ones remaining-last year the C10 on my way home from work filled up in Pimlico with families coming over to see it and did not let hardly anyone on after that so if you can walking may be a better option. Also last year they only had one side gate open at each of the main gates as searching people etc on way in. With 10 mins to go at the gate we were at there were lots of people still trying to get in and in the end they opened the main gate with a few minutes to spare so allow extra time for this
I agree with DeeDee, I was volunteering last year and was rushing people through even after the fireworks started, so get there early if you can. I'm quite surprised to hear they are one of the few free events left, that's a bit sad. They are great fireworks though, well worth the trip.