OK most of them are just normal limited companies.
Inst of Directors is a Company Incorporated by Royal Charter (England/Wales)
Inst of Certified Bookkeepers is a company limited by guarantee
VPA UK is a company limited by shares (I suspect you know this already :redface: )
However if you look at appendix A of
this Companies House booklet you will see that you can only use the name "Institute" with the permission of the
Department for Business, Enterprise and Regulatory Reform (the posh new name for the Department of Trade and Industry) as as it implies business pre-eminence or representative status