Can I travel spontaneously on a Schengen Visa?

Assuming it's not one of the rare cases of a Schengen visa with limited territorial validity, the visa allows you to travel freely within the whole Schengen area. And it doesn't matter from which country you leave the Schengen area.

A Schengen visa is always valid for the entire Schengen Area (unless it has limited territorial validity - look at the visa sticker). That being said, a foreigner should apply at the consulate of the country in which they plan to spend most time. If you plan to visit only Spain and Portugal and you submit these plans in your visa application at the consulate of Spain, you could face problems if you later change your plans and want to spend entire time in Finland. There have been instances of foreigners being turned back for such reasons (not because such visa isn't valid for Finland - it is, but the immigration officials might think you lied in your application, which makes you inadmissible). However, that's apparently not your case.

Anyway, once inside the Schengen Area, you can move freely across all internal borders. Most importantly, you can also leave the Schengen Area anywhere, incl. from a country not originally included in your visa application travel plan. As long as you're not overstaying, it won't cause any problems.

Two issues come together:

• With a Schengen visa, you are allowed to make minor adjustments to your itinerary after the visa is issued, within the duration and validity limits. That can include entering a country that was not on the list, or leaving through it.
  Typical example, you had planned to travel to Germany via France, but you change flights to travel via the Netherlands instead. Different country of entry, still recognizably the same premise.

• With a Schengen visa, you are not allowed to misrepresent your itinerary during the application. Typical examples would be adding bogus information to make a different country responsible for your application, a practice known as 'visa shopping.'

Your problem may be to convince authorities that an adjustment after the application was not a misrepresentation during the application. The problem may come up with your next visa. The magnitude of this problem will depend on your visa history, your nationality, and your residence. If you are a non-UK-national with ILR in the UK, you would probably be seen as relatively low risk, compared to some other applicants.

Most Schengen Type C visas allow you to visit any country in the Schengen Area, but bear in mind:

• That you should respect the validity dates of the visa

• That you should respect the duration of the visa

• That you should respect the 90/180 rule

• That you should respect the number of entries of the visa (for instance if you travel from the Netherlands to Spain via the UK, you will exit and re-enter Schengen, so you need 2 entries for that)

• If this is a single-entry visa, or the first trip on a multiple-entry visa, you should make sure the main reason for your trip is still the one you had on your application.

  For instance if you had planned to stay a week in the Netherlands for business, and add 3 days in Germany for tourism, that's absolutely not a problem (provided you're still within the limits of the visa).

  If you had planned to go on holiday for 3 days in the Netherlands, but suddenly decide to spend two more weeks in Germany, that may raise issues.

You can enter and exit via any country you want.

Also remember that you still must be able you fulfil all criteria for your visit: have a way to return home (ideally a return ticket, or the necessary funds to pay for it), have the required funds to support yourself, have travel insurance for the whole trip, etc.