The basis answer to this is yes -you are both liable we presume that the contract you refer to you will also have signed the Offer.Deed and the charge will be reg in joint names at land registry.(posted 8747 days ago)saying this there are various court cases over the years-some are on the website referring to the legal position of a partner regarding a Mortgage
The lender will go after the wage earner ie by Attachment of Earnings if pushed ,if both of you are not working or there is a question of illness ,then you should refer to your lenders insurance payments protection plan(presuming you have one)also you will see from the website -the rules re payment by the DSS of which the rules have changed
Should there be a reason that your partner diputes the mortgage then see a solicitor and state what grounds you dispute
Hope these guide notes help
Regards
Charles Twford