The council should release the deeds once they are signed for and proper id is obtained, but councils like to work through their solicitors, who will probably charge a not insignificant fee. The mortgage will need to be vacated, the councils usually also charge for this and require the owners solicitor to draw up the discharge. If the deeds are not required I would suggest leaving them where they are. It is likely that the deeds consist of very little more than an out of date copy folio, an up to date one can be obtained from the land registry at any time. If the property is being sold or remortgaged then a solicitor will have to be employed and the deeds taken up.