If you are on a low income then you may be entitled to working tax credit from the government to top up your earnings. You do not have to have children to qualify for working tax credit as there is credit available to you if you work a minimum number of hours a week and also earn below a certain threshold.
If you are single and work more than 30 hours a week and your income is less than £13,000 a year (for 2013/14) then you may be entitled to working tax credits. If you are part of a couple or you have children then the earnings limits are higher than this.
Check out if you are entitled to working tax credits at the HMRC website. Many people do not realise that they are entitled to this which could make all of the difference in enabling you to pay your bills etc.