But lining up against him is Alan "Howling Laud" Hope, the leader of the Official Monster Raving Loony Party, which has a 47-year tradition of fighting British elections from a standpoint of stupidity.
Dressed in a white suit, a giant white hat and a leopard print bow tie, the portly Hope has brought his megaphone to Witney High Street after a boozy time canvassing two dozen pubs the night before.
Forgetting his keys in the car door as he toddles onto the town green, the jovial Hope hands out one million pound notes and yells "Vote for insanity: you know it makes sense!"
"Those who've seen it all before, heard it all before and still don't believe it, that's the votes we pick up," he told AFP. "We bring a sense of humour, a sense of fun to something that is quite serious.
"It's a bit of good old England. I'm not sure you could get away with it anywhere else. This is democracy at its best! A wasted vote is if you don't vote at all," he explains.
"If I was to get two or three thousand votes, it would make the other parties think about getting things right, because with the expenses scandal they have made such fools of themselves."
The party, founded by the late Screaming Lord Sutch, has 136,000 members worldwide.
They are the "official" loony party to distinguish themselves from the unofficial nutters who end up running the country, Hope explained.
"I should be standing against the prime minister, Gordon Brown, but I didn't want to go to Scotland, it's too far," the rosy-cheeked 67-year-old said in his campaign headquarters -- the Red Lion pub in Witney.
"But if Cameron's going to become PM, this is where the world's cameras are going to be."
And Hope is determined to be the first to shake his hand when the results of Thursday's vote are read out.
Also among Cameron's nine opponents standing in Witney are "comedy terrorist" Aaron Barschak and historian Nikolai Tolstoy, a member of the prominent Russian family.
From Fleet, southwest of London, Hope was in a country music band before retiring in 2005 after two decades as a pub landlord.
He ran the party alongside his Cat Mandu before the joint-leader was killed in a traffic accident.
His campaigning in Witney involves "a few pints, going to the Indian restaurant and generally meeting people and making them smile and laugh. If a smile was a vote, I'd win by a landslide.
"I don't know what I'm going to be doing. If you plan things, they don't work."
As for policies, "make them up as you go along", he said. "Nothing wrong with sensible loonyism."
The party manifesto advocates rearing cattle in restaurants to cut down on transport, combating global warming by putting air conditioning outside and making poets apply for a poetic licence to curb shoddy verse.
But many of their once-loony ideas, designed to poke fun at existing rules, are now the law, such as 24-hour drinking, votes at 18, commercial radio and passports for pets.
Their other candidates standing elsewhere include R. U. Seerius, Lord Toby Jug, Monkey Drummer, Baron Von Thunderclap, Crucial Chris, Top Cat Owen, Flying Brick and Eddie "Elvis" Vee.
The leader is philosophical about his chances of beating Cameron.
He said: "Of course I'm not going to win the seat, I'm not loony enough to even think I'm going to.
"We'll see if we can have a victory party the night before."
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