Are we a Trust or an Unincorporated Association?

The church in which I am a Minister is a registered charity. According to the Charity Commission Register, the Governing Document is a Constitution. One of the Articles of this Constitution states that the Trustees will 'function according to the requirements of the Trust Deed'. The Trust Deed has been lost and a request has been made to denominational headquarters to search for a copy in their archives.

I have read that trusts have Trust Deeds whereas Unincorporated Associations have Constitutions, so I am confused about what our legal form is likely to be. The Constitution was adopted in 1994 and amended in 2006. The church has its own building and from the accounts it looks like the charity is the owner. The purchase was made around the same time, 2006. The denomination is a fellowship of self-governing local churches.

I have some weightier concerns about the constitution and a lack of adherence to its terms, but I would like to ask first of all what our legal form is likely to be? Thanks for your help.