Good Luck...
It varies from company to company and country to country. Generally you'll be looking at a degree in engineering or related discipline as a good starting point. A TP qualification from a recognised Test Pilot School - any of ETPS, USAF TPS, USN TPS, or the FAF TPS is generally a pre-requisite on your CV, latterly for civilian test flying the year long course at NTPS in Mojave will also work. Then you're going to need somewhere between 750 - 2000 hrs as PIC.
You don't need a miltiary background but financing all of the above whether through company sponsorship or by yourself is going to cost somewhere north of of half a million pounds.