Open General Licences (OGLs) involve a registration process via ECO's SPIRE export licensing database.
As a result, in most circumstances, there is no upfront requirement to obtain an undertaking.
OGL holders are required however to adhere to all the specified terms and conditions. This includes keeping certain records as required by the licence for the controlled goods and technology being exported. For more information see compliance and enforcement of export controls and an introduction to open general licences (OGLs).
If you hold the Open General Export Licence (Military Goods) there is a specific condition to demonstrate 'permitted use'. For this purpose, ECO have issued a template undertaking for this particular licence. For more information see OGEL (Military Goods).