Ticket with an extra letter in my last name

Is this your plane ticket? If so, call the airline.

If it is your airline ticket, its hard for anyone here to know what security might do on the day you go through, if there is a difference between your passport and the ticket.

Did the airline make the error? Then they should fix it.

If you or your agent made the error, you might be able to get it corrected by paying a fee to the airline, rather than buying a new ticket. Depends on the airline, what they might do for you and how much they charge.

Strongly suggest you get it resolved before the trip. You could end up being denied boarding and have to buy a new ticket, assuming space is available, at the 'walk up rate'.

Julie, This is nothing to do with customs
(a) Customs is after you land.
(b) There is no customs between Spain, the UK and Ireland because they are all in the EU.

The problem will be the airline, they are supposed to check your passport against the name on the ticket at check-in or boarding. They never used to do this in the good-old-days, air tickets had no name on them, same as rail tickets.
Who made this mistake? Was it the Travel Agent, if so you should insist they re-issue the ticket.

Otherwise I would contact the airline ASAP, and make sure they have a note on their file. And print out the e-mails to show at check-in.

DO NOT take your birth or marriage certificates with you, nobody will want to see them. Only take your driving licence if you will be driving.

I second Chris, do try to fix it with your travel agent if you can.

However, and despite indeed you "could" be refused boarding if your ID doesn't exactly match your boarding pass, I must say, I've been in your shoes at least a couple of times during my years of flying and I've never really had a problem, other than the minor nuisances of "being told" that you should have..., if this helps.

Who made the error? Whoever it was needs to correct--and pay the fee. You may be left in Barcelona.

my bersa tific it

I can see where the misspelling came from....

Within Europe airlines usually require passport details to be registered online for each flight in-advance (a few will slow everything down at check-in). Who are you flying with?

A story, probably an urban myth.

A certain Herr Müller (Müller is the most common German name) needed to fly from Germany to a small town in the USA for work. This involved one flight on Lufthansa to Chicago, then a second on a US domestic airline to the small town. All went well on the way out, until he had to check in for the return flight in the small town airport. The check-in person refused to check him in because it said "Müller" on his passport, and "Mueller" on the ticket. He tried to point out that the US airline's website would not accept the letter ü when he tried to type it in, and the correct alternative according to German spelling rules is to use ue instead, hence Mueller. The check-in person didn't believe this, and didn't believe ü was a letter as she didn't have an ü on her keyboard.

According to the version of the story, he either had to buy another ticket as far as Chicago, or they had to phone the airline's HQ before he was believed.

Conclusion: It probably will work with one letter different, but it is best to get it changed, especially if it is somebody else's fault, rather than risk a problem from a pedantic employee.