If you are travelling to just 1 country, you must submit your application to that country’s Embassy in the UK.
Example:
You plan travel for 7 days, arriving in Madrid for 4 days and visiting Barcelona for 3 days before returning home. In this example you would apply to the Spanish Embassy, as Spain is the only country you are visiting.
If you are travelling to more than one country, you should submit your application to the Embassy of the country where you will spend the majority of your time.
If you plan to spend an equal amount of time in several countries, you should submit your application to the Embassy of the country you will visit first.
Example 1:
You plan travel for 9 days, arriving in Paris for 3 days, visiting Madrid for 4 days and Berlin for 2 days before returning home. In this example you would apply to the Spanish Embassy.
Example 2:
You plan travel for 10 days, arriving in Paris for 5 days and visiting Madrid for 5 days before returning home. In this example you would apply to the French Embassy.
Depending on the Embassy, you will need to apply either on-line, in person or by post. Some Embassies will want you to apply through an agent or other 3rd-party organisation.
Each Embassy is different and it is important that you make your application in the way that they prefer.