Forget those unofficial cannabis cards. You need a formal specialist...

https://blogfreely.net/gertonmhvf/how-strict-is-the-uk-about-controlled-drug-importation-a-practical-guide

Forget those unofficial cannabis cards. You need a formal specialist prescription from a private clinic, as the NHS rarely provides this. Always gather your medical records first. Be very careful with local laws before you travel abroad with your medicine