What is the best way to warm up ahead of a race?

This can be very hard when event organisers have schedules to stick too. so 9/10 this could be no warm up in the water.
This could also result in transition being closed and you find yourself standing around waiting. So what can you do.

No warm up swim allowed so light jog: if you can have some spare trainers, then go for a 5-10min light jog. Look to roll your shoulders too whilst running as this is purely an exercise to raise the body temperature ahead of getting into the water. Look to stretch the working muscles. The wetsuit will get you warm but the water temperature might take this away. So bare that in mind.

5 mins: if they give you time to get in then think about the water temperature. If it’s cold, then get in at the last possible minute. Treading water when it’s cold is nasty and all the good work done in the landslide is taken a way. So you might as well stay warm before the start. If you can swim with do a little warm up. 2mins of gentle swimming followed by 3-4 short fast efforts. I like to do the fist drill (swimming with clenched fists) to promote better feeling of my hands & forearms then the horn goes off.