Joint Assessment Question ??

Hi I have been married since 2006, we are both assessed seperately not as a married couple. I am currently on maternity leave so not using my Tax credits & since 2009 have only had part time or casual work and not earned enough to even be taxed. Would we benefit from joint assessment & can it be back dated to date of marriage also how do I go about it? Sorry if this is a repeated topic. Thank You

Looks like it would be more beneficial to be jointly taxed