You should not have any problem in London - since you will be staying airside - not actually entering the country.

However, you may find you have problems trying to leave Spain. It is extremely likely they will check your passport to get on the plane in Spain, find you have overstayed and you may well have to pay a significant fine and be banned from entering Schengen for an extended period of time. Also - they may not allow you to go to the UK - but insists that you return right to the US.

If your trips outside Spain have been to other Schengen countries, that would explain why "Spain does not check very closely". If I were you I would check with the US Embassy for likely consequences, as a one year overstay in Schengen is more than a small oversight.

If you do make it to London and have only a few hours layover you will stay airside and not go through passport control there. Your problems, if any, will be when you exit Spain.

Your passport will certainly be checked when leaving Spain as you leave the Schengen area. Unfortunately there is no possibility leaving Spain for the US without having your passport checked, no matter which airport you transfer at. At European airports, flights to non Schengen destinations always depart from gates located AFTER immigration check points.

The US Embassy has no say in this issue whatsoever. Should the OP actually reach someone there, all they could do is speculate, about as valuable as any advice given here.

My advice is that you should be well prepared that you might get in trouble when leaving Spain. I think the immigration authority will find overstaying with one year quite serious.

Apparently standard procedure when caught overstaying a Schengen visa is immediate deportation at your own expenses. However, this is not a problem for you as you want to leave anyway. But there is also a risk that you will be fined on the spot at the airport and fines seem to be hefty (other people have reported 500 - 700 Euros on different web sites). You might also get a "Schengen Information System alert" entered in the SIS-system meaning that you will not be allowed entry into any Schengen country for up to a maximum of 5 years.

Cathinjoetown wrote:

"The US Embassy has no say in this issue whatsoever."

True, but they may be able to provide helpful advice. If not the US Embassy, where would you recommend the OP goes for advice, or are you suggesting (s)he just wings it? There are immigration lawyers, but they will likely charge a fee.

Extrava87, for such a potentially serious matter, I wouldn't rely on advice from anyone on a travel forum, including me. If the US Embassy can't help you, they may be able to suggest someone who can.

Heimdall,

"where would you recpmmend...."

An immigration lawyer (Italian based) or the Italian authorities.

<<do you think there will be a problem once they see I have overstayed my visa? >> I certainly hope so.

It always amazes me why some well educated young westerners think laws only apply to other people and willingly become illegal immigrants.

The OP has two choices:
1) stay in Spain for the rest of his/life and never try to cross a border again or
2) expect a large fine and a ban on returning to the Schengen area when he/she leaves. The UK won't fine you, Spain will (and they need the money).

An immigration lawyer (Italian based) or the Italian authorities.

It would probably be better to find a Spanish lawyer, lol! The embassy may be able to suggest one.

Much as it pains me to say it you will probably get away with breaking the law and leave Spain without a hitch.
Should the Spanish Immigration officials decide to deal with you then you can at the very least expect a stamp in the passport banning you from re-entering the Schengen zone for a number of years.
Once you get out of Schengen and into Heathrow you will not have a problem. You will stay airside and transfer to your fight home without seeing an immigration official.

Oops

I think at this point the OP realises (s)he made a mistake, and needs support rather than condemnation. I do hope that hetismij2 is right and Extrava87 gets only a slap on the wrist. I still say it would be best to get some sort of advice before turning up at the airport, though. The embassies aren't there to bail out US citizens, but do provide some services. That would be my first port of call: http://madrid.usembassy.gov/citizen-services.html

Sorry Heimdall I disagree. I have more regard for illegal immigrants escaping war and persecution than affluent westerners playing the system. The OP knew they were illegal. didn't care, and deserves more than a slap on the wrist.

Sofarsogood, if that were your son or daughter would you be saying the same thing?

>>Sofarsogood, if that were your son or daughter would you be saying the same thing? <<

Yep - I pretty much would.

I agree the US Embassy has no dog in this fight . . . Unless the OP ends up in jail (unlikely) and then they may send a rep if requested to make sure human rights aren't being violated.

The US Embassy wouldn't get in the middle of this since it would be a dispute between the OP and Spain, nothing to do w/ US laws.

<<if that were your son or daughter would you be saying the same thing???

Yes, because it would teach them not to be so stupid in future, and to take responsibility for their actions.

But to return to the OP's concerns, no one on this forum knows the answer to the OP's question. The only way they will find out is when they attempt to leave; and with each and every passing day, they're making it worse.