I recently attended a meeting of the Clipsham Yew Tree Avenue Trust (CYTAT) – the charitable organisation that now has the licence to manage and maintain this historic avenue.  Many of the trees are more than 200 years old and the site is owned by the Forestry Commission, who maintained the various topiary designs until 2010, when funding was withdrawn.  More information can be found here: https://yewtreeavenue.co.uk