According to 'The Smugglers of Christchurch' by E.R. Oakley this structure was a mausoleum of a certain Mrs. Perkins who died in 1783.
This lady had a horror of being buried alive and requested that her body should not be interred, but that a fabric should be erected to receive it near the entrance to the free school then in St. Michael's Loft of the Priory. So that the boys should hear if she revived, she also requested that the lid of the coffin should not be screwed down, and the lock of the mausoleum constructed so as to enable her to open it in the spring. These wishes were carried out, but when her husband died in 1803 her body was removed. The structure sold and re-erected on this present site.
Former mausoleum - Priory Gardens, Christchurch, United Kingdom