1999 Ford Focus intermittent starting problem

Hi as I am new please bear with me.

I can drive my focus around town without any problems then for some unknown reason after a short stop it won’t start at all. I can turn the key in the ignition back & forth & there will be no response from the engine. The battery seems ok as the radio & everything else seems to work. The strange thing is that after 30 to an hour you can turn the key in the ignition & it’s as if nothing happened. Engine turns over ok not a problem.

This has now happened to me 3 times now twice I called out the RAC / Green Flag & after a period of looking at the car just tuned the key & it started. The third time it happened I left if for an hour it started & got me home.

Spoke to my mechanic & he said it could be anything & as the fault only happens now & then it is hard to tie down to what it actually is.

HELP

I would like to get this sorted before xmas but would like to avoid me paying my mechanic a fortune to change EVERYTHING in the car without finding the actual problem.

Thanks