Typically, as well as a bonus code to activate the offer, there will be wagering requirements that you need to meet before you can withdraw any winnings from the no deposit offer. These will usually involve you playing through any winnings from the £5 free credit a certain number of times. So, for instance, if the offer has a 3x rollover requirement, and you won £12 you would have to play through £36 before you take any of that money out if you chose to.