Just got an email from the RPHM organisers. There’s an app in the Google Play store that allows you to track the runners (including me) during the race, and also provides split times as they run over the timing mats. For runners, it also shows you where you are on the course at that time. Although I wouldn’t recommend it — you need to make sure you’re not running into the barriers :D

Google Play: http://royalparksfoundationemail.org.uk/1L97-3PL8Z-ERXF5H-1SKAD2-1/c.aspx