Hi, here is the guidance from Volunteering England.
Job Seeker�s Allowance
People on JSA can do as much voluntary work as they want as long as they remain available for and are actively seeking work. This will mean that they will have to show that they are looking for work and applying for jobs where appropriate. If an individual is volunteering, then they are entitled to 48 hours� notice if they are asked to attend an interview, and a week�s notice before starting work. These are concessions to the 24 hour notice normally allowed.
I hope this helps. It' s a great idea to volunteer whilst looking for work. Not only does it broaden your experience, it will also boost your confidence and as you rightly say, enhance your CV. Speak to your local volunteer centre (can be found on Volunteering England website) or wisit www.do-it.org.uk.
Best of Luck!