In a London hotel, the best of enemies share a day of unbearable tension

A Slice of Britain: Like England's 1966 football win, there was an awful lot riding on yesterday's cricket World Cup Final. And it was just as frantic in London as Mumbai

It's only 8am and my nerves are already jangled. The cricket world cup final in Mumbai means an early start for London's hardcore India and Sri Lanka fans, who arrive early wearing regulation jester hats to get peachy seats in front of the London hotel's huge projector screen.

This is a cricket final subcontinent style, so everyone is digging into an Indian and Sri Lankan breakfast buffet – curd rice, spicy eggs and chicken curry – as the first ball is bowled. It's the 10th world cup, and the match promises everything: home interest means the stadium crowd is besides itself with nerves and hopes and dreams; the best two teams of the tournament have made it through, and there's no shortage of sentimental and romantic possibilities. India's Sachin Tendulkar, 37, Mumbai's Little Master, is hoping for his 100th century on his home ground. Sri Lanka's master spin bowler, Muttiah Muralitharan, 38, is playing his last ever international match. To have these two statesmen playing against each other for the last time, in a world cup final, is a cricket fan's dream.

At the London hotel, brothers Kivan, 39, and Gaveeka Fernando, 32, were among the first to arrive from their Essex homes with their mum, wives and children. Born in Negombo, 23 miles north of Colombo, they came to the UK 18 years ago as economic migrants. The family is firmly Sri Lankan when it comes to cricket, though ardent England fans in every other sport.

Kivan's nine-year-old son plays cricket. He's an all-rounder for the Essex under-nines, which could make things a bit tricky supporting wise as his dad is convinced he'll be playing for England one day.

As the game gets under way, Gaveeka, an investment banker, lets his nerves show. It doesn't go down well with his brother. "In my heart, we will win, but in my head, well, I think India might have the edge. Maybe." As the first boundary of the match finally happens in the sixth over, the whole family leaps up, and maracas and tambourines are shaken. "We'll definitely win," says Gaveeka more confidently. Next ball, a batsman swings and misses, the room gasps and Gaveeka looks forlorn. Who says cricket isn't exciting? The fools who don't get it, that's who, and there are still more than seven hours to go.

But, if we think it's tense here, it is strangulatingly taut in the stadium in Mumbai. Inside are 32,000 fans; inside and out are more than 3,000 police officers and paramilitaries. None of them needed reminding that this is the city of the notorious terrorist attack that killed 166 people. Both teams stayed in the Taj Mahal Palace hotel, rebuilt after it was partially destroyed in gunfights involving the attackers in 2008.

But sport is nothing if it is not therapy, and this was a day for an entire subcontinent to get some treatment, albeit of a testing nature. While 20/20 cricket is all about big hitting and cojones, and Test matches are as much about psychological strength as physical, the 50-over one-day matches have it all. Excitement and tension intermingling together like a first date, wedding and divorce on the same day.

Right at the back there is a group of twentysomething boys who know each other from "home", Colombo, all working or studying in England. They've been drinking beers since 9.30am; by 1pm they're chanting "Sri Lanka, Zindabad" ("Long live Sri Lanka" in Hindi); an hour later they're in trouble for dancing on tables. These boys could never imagine supporting England over Sri Lanka in the cricket, no matter how long they live here. In rugby, the second most popular sport in Sri Lanka apparently, England is their team – a fact that may have more to do with England being their only hope, in rugby, of tasting victory.

This may be the final, but for many Indian supporters, the "real final" was won against Pakistan, last Wednesday. This could explain why the Indian fans are totally outnumbered at this party, even though the hotel is owned by an Indian family. Balwant Singh, 35, and Bhupendra Saharan, 30, don't let that stop them from cheering every Indian success. Victory doesn't have to be loud to be sweet, they insist. But when the Sri Lankans score a six from the last ball of the innings, and take an Indian wicket with their second ball, the noise is enough to kick the cockiness out of even the most ardent Indian supporter.

Tendulkar has played for India since the age of 16 and is a million times, approximately, better known than the country's Prime Minister. He isn't popular like a Bollywood star, more worshipped like a Hindu deity. Though here in Club Ten, opposite St Paul's cathedral, the Sri Lankan fans pray he doesn't score a century, a prayer someone answers in India's seventh over.

It was a setback but, bit by bit, single by single, India's other batsmen gradually bore down on the 275 runs they needed for victory. There were wobbles along the way, but not many, and the target was always within reach. It crept closer and closer, until, with a mighty heave for six by the Indian skipper, Mahendra Singh Dhoni, the cup was won. The India fans in London went briefly deranged, as did an entire nation. This, like England's football triumph in 1966, will means a great deal to an awful lot of people.