first time bike

hello everyone
im new here and am after my first road bike. i am unfortunately on a budget. £200 maybe £ 300. i know its not a lot after going into a few shops and having looked i have decided to buy second hand. i used to be into mountain bikes and trials a few years back but its a lot of hassle for me to travel to the spots now, i want to start something on my own doorstep. i have fell out of what i would call my happy fitness level as well, the smoking didnt help. im giving up should have never have started. so on top of wanting to start this as a hobbie its also a sort of fag replacement. any ideas would be welcome