Mr Clulow had been through two passport controls in Birmingham and Alicante – without anyone realising he was carrying his blonde girlfriend's passport.
The 50-year-old, from Halesowen, was heading to the Spanish resort to celebrate a friend's 50th birthday.
But in his rush to get to the airport, he had accidentally picked up his girlfriend Karen Clift's passport.
The father-of-five's mistake was only discovered after he landed in Alicante.
Mr Clulow did not notice his error when he left for the early morning flight.
He met up with 14 friends at Birmingham Airport ready for the three-night trip to Benidorm to celebrate pal Carl Fentham's big day.
Because he was only travelling with hand luggage, Mr Clulow showed his boarding pass to get through security and had breakfast as he waited for the 7.30am flight on March 16.
He said he flashed his passport to the Monarch Airlines member of staff at the gate and boarded the plane.
And after the two-and-three-quarter hour flight, he successfully breezed through passport control at Alicante Airport without a word from the Spanish authorities.
He only realised the airport blunder when he and his pals were comparing passport pictures and he discovered he had used Karen's document.
Mr Clulow said he was astonished authorities had failed to pick up on the mistake twice even though his girlfriend has long, blonde hair, and he is bald.
He added: "I handed my passport over with the boarding card when we went to board the plane and she scanned them.
"Then we got in to Spain and went through passport control and I flashed the passport and they never said anything.
"Me and my mates were joking about our bad passport pictures and they looked at mine and said 'Neil, you're much better looking in this picture than in real life'. I can't believe this could happen, especially after all the trouble with the missing Malaysian aircraft. It's astounding.
"With this plane going missing and people on there with the wrong passport you would've thought they would have been a bit more vigilant. If I can get through then who knows what else could happen. I got through on to the plane and got through passport control in Spain and didn't get stopped by one person. It's frightening.
"They need to crack down at British airports big time. It does need addressing."
Mr Clulow had to fork out £70 for his passport to be posted to Spain but was forced to wait in the hotel for the entire three-day break because it needed to be signed for.
But Mr Clulow claims the passport was accidentally sent to Berlin before being redirected to Benidorm – meaning he missed his flight home on March 19. Luckily, Monarch Airlines bosses agreed to fly him back the next day for free and two suited representatives were even waiting for him when he landed.
Mr Clulow, who has five children from another relationship and has been with receptionist Karen, 50, for 12 months, said they seemed worried how the security breach could have happened.
He claimed: "I phoned my girlfriend and asked her to send it by DHL but they wouldn't take it because it was a passport. We said it was important travel documents and UPS collected it, it cost me £70.
"They got it on the first plane but it went to Berlin. Then it was in Barcelona on the Wednesday but it didn't reach Alicante so I lost my flight. It arrived on Thursday and I flew back then. It completely ruined my holiday. I couldn't leave the hotel because I was waiting and needed to sign it and UPS kept saying it would be there and it kept getting delayed. It was a waste of a break and I lost a day of work as well because I should have been home on the Thursday.
"There were two suited and booted Monarch reps waiting with a plaque with my name on it when I landed.
"They wanted to know what happened. They asked if I would be willing to point out the woman who let me through because it was a serious breach of security.
"But I didn't want to do that to her so I refused. I've heard nothing from them since."
Monarch Airlines said today: "We can confirm that Mr Clulow was able to board a flight from Birmingham to Alicante on 16th March 2014 with an incorrect passport.
"Monarch use ground handling agents at all our UK bases to manage check in, boarding and other non-flight related tasks. At the time of this incident, the agents in place at Birmingham Airport were Servisair.
"Servisair agents wear name badges and airport identification passes clearly identifying themselves as Servisair. We have had confirmation from Servisair that they are carrying out an investigation into this incident.
"It is also our understanding that Mr Clulow made his own arrangements to have his passport couriered to the hotel in Spain.
"The delay in receiving his passport resulted in him missing his return flight, which was booked on another airline. However, the return flight was provided by Monarch, as a gesture of goodwill. We would like to clarify that the agents who
met Mr Clulow upon his arrival back at Birmingham airport were also Servisair personnel and not from Monarch.
"Due to operational reasons unrelated to this incident, Monarch has recently changed service providers for our ground handling requirements at two UK airports, Birmingham and Luton and no longer use Servisair at Birmingham Airport."
UPS said: "UPS is aware of the reported shipment and we are currently conducting a thorough investigation. UPS takes the delay of any consignment extremely seriously."