Questions have emerged over the leading theory behind the deaths of a couple who were found dead in a hot tub in Spain.

Patrick Tobin, 48, and Thomasina Tobin, 51 were discovered by their two teenage sons at Villa Luna in the Spanish city of Cullera in August.

The London-based couple were found partially outside the spa with cuts and suction marks on their bodies, with reports suggesting they may have been dead for up to 12 hours before they were discovered.

At the scene, detectives noticed a strong chemical smell and found found blood in the cloudy water.

Spanish authorities have been investigating whether a malfunction in the hot tub’s circulation system could have played a role in their deaths.

One possibility under examination is a rare phenomenon known as “suction entrapment”, where a person can become trapped against a drain or suction outlet.

But a local spa technician, Francisco Quero, who is familiar with hot tub systems, has questioned whether the equipment could have been capable of producing enough force to hold an adult underwater.

“This is a privately owned [hot tub] on private property, which means its motor runs on two or three horsepower maximum [equivalent to a large lawnmower or pressure washer],” Mr Quero told the Daily Mail.

“It is very strange that an adult would get stuck in the suction system. A baby might get stuck but not an adult.”

The suction theory has raised the possibility that one of the Tobins became trapped in the hot tub while the other died during a desperate attempt to rescue them.

But Mr Quero said he was sceptical that a fault with the protective grill covering would be enough to trap an adult.

“There could have been an electric shock, causing a person to lose consciousness and block the suction, but... it does not make sense to me,” he added.

“It is impossible to get stuck in one of these devices and not be able to get out.”

“I am not an investigator, and I have not seen the equipment but I would rule out that hypothesis.”

Police investigated whether either victim had been electrocuted in the spa but the theory was ruled out.

Mr Quero’s concerns have been echoed by CEO of Goccia Spa Carlos Navarro, who also casted doubt on the suction theory.

“I have visited factories all around the world and seen many different designs and it is practically impossible for something like this to happen at hot tubs installed in the home,” Mr Navarro said.

“The suction is caused from two holes at the bottom and both have security nets. Maybe these nets broke and the owner never replaced them.”

“It is very improbable but there may have been a chance that one of the holes became covered by something and blocked, causing all the suction to go through the other hole. But I still don’t think this would be enough pressure for an adult to get stuck.”

“There are security measures that cause [hot tubs] to switch off every 15 minutes as well.”

The tragic deaths devastated the couple’s two teen boy’s during what was supposed to be a luxury two-week getaway for the family.

Police were called to the confronting scene after the two boys alerted the villa owner, who lived nearby.

Three relatives, including an uncle, travelled from Ireland to Spain to care for the teenagers following the tragedy.

Mr and Mrs Tobin’s deaths are still under investigation by Spanish authorities and the official post-mortem findings are not expected to be publicly released.