Reg 14 [UNECE]
Belt and ISOfix anchorage tests. Belt anchorage loading + loading transmitted to seat, legs and vehicle floor. 

Reg 17 [UNECE]
M1 seat strength test.  Specific requirements/tests on seat/head-restraint to minimise injury.  Two head-restraint pendulum tests. Seat back + head restraint strength test. Dynamic test on complete vehicle.    

Reg 80 [UNECE]
M2/M3 seat strength test.  Includes dynamic belted/unbelted mannequin tests for leg, chest and head impacts with rear of seat in front.

There are 3 main approval methods for unregistered, new or converted vehicles:

EWVTA - European Whole Vehicle Type Approval
Approval for a documented vehicle ‘Type’. Rigorous testing and costly implementation but cheaper per vehicle for large quantities. Individual vehicles do not require inspection.  Manufacturer can sell the product throughout EU with no need for additional national tests.  EWVTA requires full Reg.17 or Reg.80 compliance, specific Reg.14 in-vehicle testing, and Conformity of Production (CoP). 

NSSTA - National Small Series Type Approval
A UK scheme for low volume manufacture.  Limited to 75- 500 vehicles per type, per year, depending on M category.   Individual vehicles do not require inspection. Reduced CoP requirement, fewer administrative requirements.  

IVA - Individual Vehicle Approval
Least rigorous testing/administration; most expensive per vehicle.  Individual vehicles must be presented, with documentation, at VOSA station.  No CoP requirement, no Reg.17/Reg.80 insistence and reduced Reg.14 requirement.  

ECSSTA - EC Small Series Type Approval
See link
https://www.gov.uk/automotive-import-and-export-regulations

NB: Concessions for some of the regulatory requirements are applicable for ‘special purpose’ vehicles such as Wheelchair Accessible Vehicles (WAVs).