More than 9 million people will hear the dulcet tones of a son of Shoreham-By-Sea when the Grand National reaches its climax today.

The Aintree spectacular will be particularly poignant this year for Simon Holt.

It is Holt's last National as Channel 4's lead commentator. ITV are taking over terrestrial television coverage of British horse racing from January next year after agreeing a four-year deal.

Channel 4 have been in charge since 2013, following half-a-century of the BBC holding the National reins.

Holt derives a crumb of comfort over its survival, at least until 2020, as a terrestrial TV event, unlike so many other sporting showpieces such as the coinciding US Masters, now in the grip of Sky.

He said: "It is sad. I've worked for Channel 4 since 1994 and I think they have given a really good service to the racing industry.

"Terrestrial coverage is becoming quite a rare thing in sport nowadays. It holds value.

"It might not always in the future but at the moment terrestrial television is going to get bigger audiences than on a satellite platform.

"Contrary to what some people believe, not everyone has Sky and doesn't have access.

"I think it's been a great thing. Channel 4 Racing, for all these years, every Saturday without fail, has given racing a shop window to a large audience.

"Times are changing. The landscape is changing, as we have seen. Our viewing figures have gone down for the last couple of years but they are still considerably higher than for other sports that have disappeared.

"It's a difficult one for the rightsholders of these sports. They have either got to take the money from Sky and sacrifice audience - and they can put that money into the grass roots like cricket has - or get the audiences on terrestrial TV and be poorer."

Holt will be calling the winner home later than usual. The National has been put back an hour this year to 5.15pm, after football has finished, in a bid to boost viewing figures as Pulborough-based jockey Leighton Aspell aims for an unprecedented hat-trick of victories aboard last year's victor Many Clouds and Albion chairman Tony Bloom for an upset with his outsider Aachen.

Holt, who wrote for the Sporting Life before picking up the mic, said: "It hasn't gone down too well with some print journalists, due to copy deadlines, but it will increase the audience size, which is very important for the sport.

"This is the biggest audience race of the year and if it comes at the end of a football match we will hopefully have a bigger audience to see possibly history being made if Many Clouds can be the first horse since red Rum to win two.

"When you look back on Red Rum's achievements, he was absolutely remarkable. He won three Grand Nationals. No horse has come close to winning it a second time since.

"In fact, up until this season no winner since Bindaree in 2002 had ever won another race since winning the Grand National. And yet Red Rum came back five years running and would have come back a sixth year had he not injured himself just before the race, so he was an amazing horse.

"I think Many Clouds is a real contender. He jumps brilliantly, he's had a brilliant preparation, stays and he's got a bit of class. It's a real possibility and I hope it happens."

Holt, approaching his 52nd birthday, has commentated on countless races since launching his career in the industry as a teenager with a small publishing company in Shoreham and becoming a racecourse voice in 1988.

There is nothing quite like the National though, so the self-proclaimed film buff, bookworm, cigar-smoking wino (according to his colourful Twitter account biography) could be forgiven for puffing on a Havana and downing a glass of vintage red once it is all over.

"It's quite a challenge, because you've got 40 runners in the race," he said. "There's quite a lot of pressure, because it's a very high profile occasion and a lot of people are watching at home.

"It's harder on the first circuit when more horses are running. By the second circuit they've thinned out quite a bit.

"The hardest thing is spotting the fallers, all the incidents that take place. There's a lot of luck whether you are looking in the right place or not but it's a privilege to be able to commentate on the race."

The job is too big for one man, even a man of Holt's experience and expertise.

He said: "There are three commentators on Channel 4, one located near the third fence as they go down towards Becher's (Brook), then another one on the Canal Turn, then I pick it up from Valentine's (Brook), because the course is so huge.

"Also, because the race tends to take about nine minutes to run, that's a lot of time for one person to speak at pretty high volume but also for the audience to listen to one voice. I think the change of voice adds to the drama.

"Traditionally it was always commentated on by three or four on the BBC and Channel 4 have adopted the same system. I think it works okay - and I'm the lucky one that gets to call the finish when it's easy!"