From the internet:
Understanding the myth of common law marriage
Contrary to popular belief, there is no such thing as a ‘common law marriage’. In England and Wales only people who are married, whether of the same sex or not, or those in civil partnerships can rely on the laws about dividing up finances when they divorce or dissolve their marriage.
The assumption by many unmarried couples in a long standing relationship that they have acquired rights similar to those of married couples is wrong. This common misconception needs to be addressed particularly as for many years official statistics show numbers of marriages in decline as more people choose to cohabit (living together without being married).
Many people also believe that by having a child together they acquire legal rights, whether married, in a civil partnership, or not.
This is also not true. Although there is scope to apply to court for financial provision when there are children, such orders are made for the benefit of the child and only couples who are married or in a civil partnership acquire legal rights and responsibilities in relation to each other.
Your rights if you split up
For couples who are not married or in a civil partnership, if you split up your partner would not (except in certain types of cases) have to pay you maintenance even if you stayed at home to look after your children – but they would still have to pay child maintenance.
For couples who rented together, if you were not named on the rental agreement you will have no automatic right to stay if they walk out or ask you to leave and you would be left to apply to court for an order giving the right to occupy, the outcome of which is uncertain. If your ex partner owned your home, and there is no other agreement in place, you have no right to stay if they ask you to leave.
Similarly, if you are not married or in a civil partnership, any savings or possessions your ex acquired out of their own money will not be shared with you although lump sum orders can be made in certain circumstances in proceedings where there are children.
To protect yourself if anything happens, you could consider entering into a contract with your partner to decide how money and property should be divided if you separate. These are known as "Cohabitation Contracts" or "agreements" and can be drafted by a solicitor.
http://www.familylives.org.uk/advice/your-family/relationship-advice/common-law-marriage/