What time of day are you planning this? Running along the south bank can be awful, unless you like dodging people!
I ran that route (or parts of it at different times) a lot when working in London. I mostly stayed on North bank as it was quieter and easier to just get into a rhythm and run, rather than getting caught in bottle necks and having to dodge people.
On the north, you have to come away from the river briefly around St Paul's. But think it's pretty well signed with arrows for riverside path. You also have to leave the river a Parliament (also a very busy stretch) and as Bear says at Battersea. Though you can lose some distance here by running along the A308 (new king road) which I found quite nice to run along with some bars and shops to look at! From Putbey Bridge to hamnersmith definitely run along the south bank as it's nice, easy and off road.
On the south bank, Tower bridge to vauxhall is easy to follow, interesting, but is busy (unless you're going early in the morning). I found I was pushed away from the river at Vauxhall, but I think it was due to building works. Maps certainly show the riversides walk here. No experience it running Battersea to Putbey on the south as I always went North here due to fitting in with my distance plans better!
Thanks for all the advice.
Target time was 7.40 but that was gonna be a stretch for me on a good day, and with today's temperatures it was not gonna be a good day!
I was in a heat with about 20 people, thought they were mostly going to be faster than me so settle in at the back. Once garmin settled down I check pace, and quickly realised That despite being last, I was going to need to slow down as I was well under target pace and feeling it. Next, just to make things worse I realised my shoelace was undone! First lap 3:53 (including s stop to tie the lace). Second lap was uneventful, managed to catch a couple of people and tried to sprint for the finish, felt like I'd picked uo, but was actually slower. Final time 7:55.
What I leant, probably not going to get my best time on a hot day, i probavly need to hang back further at the start, and make sure to tie my laces!
Thanks for all the responses. Lots to think about. I like the sound of starting just a little slower than target pace and then evaluating. They start us in waves with similar target times. If people have similar strategy to me, it will help to have someone the aim for on the way round, just got to make sure I don't get myself pulled away too fast at the start!