Question Author
Thanks themas for your reply and in response to your very valid points.
Unfortunately we agreed to the proposal by the estate agent, who also have a letting section - believing that we were being helpful to the Seller. That was before engaging the conveyancer who had previously acted well on behalf of another family member. Throughout, the conveyancer has distanced themselves from it, so I'm afraid we don't feel we have any comeback on them.
Since posting this query, we have found this website <http://www.landlordzone.co.uk/blog/legal-bri
efing/license-or-lease>
which says that a House of Lords ruling back in 1985 makes it clear that even if the words in documents referred to a Licence, a sole occupancy would in fact be a Tenancy.
So it looks like a Tenancy Agreement is needed.
Sam