Spectator cost is zero – yes it’s free to enjoy.
Race venue is Parliament Hill Athletics Track, Hampstead Heath, London, NW5 1QR.
The track is based within beautiful Hampstead Heath so great for pre event picnics and walks, for more info
In terms of transport links it is easily accessible from central London and quickest option is usually to use the underground via Northern Line to Belsize Park or Kentish Town stations. See map below: