Labas vakaras,
I'm a Moroccan man and my wife is Lithuanian (but she was living in LT not in UK).
It is much easier to get married in Morocco, then register your marriage in UK. It is less expensive (regarding fees) + your husband-to-be will have more chances getting a visa to live with you in UK if you're planning to settle there.
No need to remind you of Moroccans who get married to foreigners just to get a way out of Morocco (no disrespect, I just heard of a lot of bad stories like these, and being a Moroccan man, it makes me very sorry, because I know that when Lithuanian women love, their love is real!! LOL)
Look for "Marokieciu zmonos" on facebook, women there will be very helpful. Also "Lithuanian-Moroccan marriage" is a little group I'm running where there are a few useful links.
Find out a list of documents to provide for a permission for a mixed marriage in Morocco
here
There is also
another post in this section about the same issue, read what I wrote there as well.
Iki.