The first thing most runners consider is how long is the race. Then, most want to know if it is has been accurately measured so they can evaluate their performance and especially if they hope to achieve a personal best.
You will need to get your race measured by an official course measurer and then you will be issued with a UKA or ARC Certificate of Course Accuracy as appropriate. Official measurement is a condition for the issue of a race licence by the governing bodies. The only UKA or ARC races which do not need a certificate are those which do not advertise a distance, or those which are multi-terrain and therefore can not be guaranteed to be accurate.
Have you worked with Association of UK Course Measurers for your event?