Start off with a 1.1 nova or fiesta of similar, maybe a ford ka, these are going for approx £1500 nowadays and think they are all newer than p reg. This will offer you cheep insurance too which is the first thing you need to consider. Build up your no claims for a few years then move on to something bigger and better.
It does take time and you can just jump into a rapid car straight away (look at me, im still paying £1300 insurance with 5 years no claims and im an old get)
Im sure people will give you the same insurance advice as i have.
Good luck car hunting lol