A-n insurance is to 5m not 2m and covers pretty much everything that you could need but I am not sure it actually covers workshop contents in the way the original post requires. Here's the wording as in the policy
This policy is only operative while the Artist member is undertaking the following
activities in connection with their visual or applied art practice:
(a) the making, developing, designing, creating, preparing, installing,
selecting, exhibiting, presenting, display and sale of any works of visual or
applied art (including works made in collaboration with others or work not
created by the a-n Artist member)
(b) the lecturing, teaching or demonstrating of visual or applied art including
(but not limited to) workshops, residencies and community projects