Kill all the sources of ingredients and you have a long term problem. Those of an evil disposition will be aware that the Queen and her Council can have a good guess at what spells you will use given there are only so many magical ingredients available to anyone.
The Queen and her Council reserve the right to magical self defence. Those of an evil disposition would be better off changing their opinion.
Those in direct service to the Queen and her Council will keep their specialist skills up to date at all times. They will prove their prowess with these skills at times to suit the Queen and her Council.
It is expected that time to practice these skills will be taken outside of any Council or other official duties due to be carried out by those affected by this ruling. In other words, no skiving off to get your practice in!
If the Queen and her Council feel more practice sessions are needed, this will be accepted without argument but you can be assured they will not ask for these without due cause. They are not in the business of winding people up. That gets left to the sprites.