On a more positive note.
The restricted License is a leftover from when the old UK CAA system transferred over to JAR66/EASA.
Some countries transferred their old licence straight over to the new without restriction. The UK CAA didn't as the requirements were/are different. The consequence is that there are many LAE/Techs in the UK with restricted licences who certify using 'grandfather' rights.
You cannot gain a restricted licence today, you must complete all the modules and experience requirements to gain an unrestricted licence.
I think. No doubt some smart arris will jump in and put me right.
Hope this helps, good luck.