random non starter

My gti sometimes doesn't start.
There is no rhyme or reason to it, i went on a 75 mile run today, absolutely fine.
Started up, drove home, dropped son off, went out to park car and nothing. All i got was a click from the number 17 relay (which was warm) and nothing from the starter. Hit the starter for a bit but no different, went indoors, had a cup of tea, went out, started first flick of the key.

It has done it once before but i had only been on a short journey that time…

Confused.

I would check the two wires going to the starter making sure they have good connections,you could connect a volt meter or even just a bulb to the trigger wire [thinner one of the two] to see if you have feed there when you turn the key,also check the earth cable which is bolted to the gearbox,try these first to see how you get on

Sounds like a sticking starter motor solinoid to me.  Get a second hand one and try it, or take yours off and get it refurbed maybe.  

I had the same fault and I could solve it in the short term by giving it a technical tap with a hammer every time it played up.

whacked a new starter in it today, seems fine......until the next bit falls off!!