Calculating average distance between multiple points

[AfterEffect]

I have a Google Map with 300 place markers on that comprise of places around the UK (also have as KML).

I need to calculate the average distance between points (i.e. if you was at one point, on average, how far would you have to travel before you get to the next point).

Does anybody know how on earth I could do this?! (sorry if it's in the wrong forum!)

 

[AfterEffect]

We're looking into doing a 'order online, collect in-store' and want to add a 'On average people only have to travel x miles to get to one of our storse!' selling point to it

I guess from above the working out the distance from 1->2 2->3 3->4, etc and then /300 would be good... but I really don't have the know how Was hoping there may have been a site out there that did it already but Google has failed me on this one