Here is the link I found on the Embassy website:
Assuming that you are a UK citizen and your wife has a BRP and you are travelling together the visa should be free and expedited showing minimal paperwork. It should take no longer than 15 days, if i remember correctly.
You should be able to go directly to the Embassy and not BLS. I found a line of text on the website but I can’t find it again. The Embassies do tend to bury it so that people feel that have to go via BLS. I would send them an email requesting a direct appointment or ask how you get a free visa via BLS.
This is the link to the application form PDF.
Note the following:
* The fields marked with * shall not be filled in by family members of EU, EEA or CH citizens (spouse, child or dependent ascendant) while exercising their right to free movement. Family members of EU, EEA or CH citizens shall present documents to prove this relationship and fill in fields no 34 and 35.