· Britain experienced its hottest July day on record last week and forecasters say more is to come as climate change tightens its grip on the country · Global warming experts claim that by 2050 temperatures will regularly top 40C and warn that our health and infrastructure will be unable to cope

They were the images that finally demonstrated the irreversible climate change now taking hold in Britain. Where green parklands once provided cool refuges in our cities, newspaper photographs last week showed them to be bleached, white landscapes. Reservoirs were revealed as cracked, arid deserts. And from Cornwall, pictures of the nation's first cage-diving trips for shark-watching tourists, an experience normally confined to Australia's Great Barrier Reef.

In addition, schools closed, steel railways buckled, and road surfaces melted. And finally, last Wednesday, the temperature reached 36.3C, the hottest July day on record. Once more Britain experienced a scorching heatwave, the fifth bout of intense summer heat to have struck the country in 10 years. And the weather forecaster says there is a lot more to come.

By any account, the searing conditions experienced last week are just a mild foretaste of the severe climate changes that lie ahead. Even if the world's carbon dioxide emissions reached the levels sought by the Kyoto protocol, there is nothing that can be done to halt global warming.

As a result, by 2050, very hot and dry summers will occur once in three years, according to the UK Climate Impacts Programme, while maximum temperatures will top 40C. By 2080, south-east England could become on average 5C warmer in summer, making it as hot as Bordeaux today. The whole of the UK would be affected, although the south-east will bear the brunt, with London taking the worst hit because of 'urban heat-island effect'.

Climate change will affect how we eat, drink, work, holiday and build our homes and offices. 'We're going to have to get used to 30 to 40 days a year with temperatures above 25C,' said Ian Curtis, leader of the Oxfordshire Climate Exchange Project. 'It's going to be weird. In our offices, photocopiers and computers are chucking out heat. We need to give people a signal of how much energy they're using, making the electricity meter visible instead of hidden under the stairs.'

Siestas, going home in hot weather, taking longer holidays and working in the cooler north of Britain have all been mooted as possible remedies. Increases in road rage and violent crime have been identified as dangers.

Global warming is also interfering with the rhythms of British nature. According to projections obtained by The Observer, wheat production will be down this year by nearly a million tonnes because the severe drought has damaged crops and forced farmers to start harvesting early. Giampiero Genovese, of the European Commission's Joint Research Centre, said: 'The wheat-ripening phase has accelerated very fast, which means the grain will be small, and if there is heat stress - 30C for several days - the wheat can even be empty. The UK is on course for a loss of 5 per cent compared with last year and if, as we predict, there is another heatwave, it may be even worse.'

The British wine industry, however, is revelling in the new climate. Last week Nyetimber Classic Cuvee 1998, produced in Sussex, was crowned the best sparkling wine in the world outside the Champagne region of France. The soil and climate in south-east England are now almost identical to those of Champagne, and tourism leaders believe winery tours could take off. Last month, in another symbol of Britain going Mediterranean, the country's first olive grove was planted in Devon, while fields of lavender are becoming a common sight in Sussex.

This could also mean the demise of the English country garden and lawn. The Royal Horticultural Society warns that daffodils, bluebells, snowdrops, crocuses and tulips will all suffer, as well as birch, willow, ferns and mosses. Gardeners will find it easier to grow exotic fruits and sub-tropical plants. The reproductive patterns of pests could change, meaning more flies, rats and mosquitos.

Human health is therefore at risk as well. The heatwave in 2003 is estimated to have caused around 2,000 extra deaths in England and Wales and 15,000 extra deaths in northern France. Last week's heatwave in France is estimated to have killed 21 people, including a 15-month-old baby. And then there is the impact of the heat on Britain's ageing buildings which were never meant to withstand such a climate. Chris Twin, of engineer Arup and an adviser to the UK Climate Impacts Programme, said: 'As things stand, the majority of buildings will need to be torn down or installed with air conditioning.'

However, the energy consumed by air conditioning could accelerate climate change further. As Ian Curtis urged, Britain must meet the challenge before it is too late: 'It needs an explosion of creativity across society to deal with these things. We're in a tight spot and we need imaginative minds.'

But with temperatures set for the mid-30s again this week, the big heat goes on.