Starting at parkrun level got me to my first fell race last year and have joined a club that mainly does fell/XC/ultra (that said I'm more road/XC). I think they're absolutely brilliant, my only qualms are with the sponsorship but am willing to look the other way. Admittedly this thread is six years old and the continued co-existence of parkrun and local 5k/10k events (and indeed their blossoming!) shows the answer.