At least the fortune tellers saw it coming. The biggest overhaul of consumer protection laws in 40 years comes into force today with tighter controls on all sorts of traders, from pushy double glazing salesmen to clairvoyants and tarot readers.

More than 30 types of unfair sales practices are now banned outright as loopholes currently exploited by unscrupulous traders are closed off.

Making misleading statements, using fake credentials and employing aggressive sales practices are all now illegal under the new rules.

Among the other tactics no longer permitted are bogus closing-down sales, limited-time offers that are later extended and false testimonials on websites. High-pressure sales techniques which are likely to harm the elderly or vulnerable are also banned.

The changes in the law have been introduced to comply with a European Union directive aimed at forcing traders to deal fairly with customers and potential customers.

Under the new laws, which will be enforced by the Office of Fair Trading (OFT) working alongside local trading standards officers, any trader or business found in breach of them will face substantial fines or even prison sentences, depending on the seriousness of the offence.

While the laws are welcomed by consumer groups, they have not found favour with those working in the UK's multimillion-pound psychic industry.

The regulations force mediums, astrologers and clairvoyants who charge money to tell customers that their services are "entertainment only" and their work is not "experimentally proven".

Carole McEntee-Taylor, 50, a spiritualist healer and spokeswoman for the Spiritual Workers Association, said: "They are asking us to prove our beliefs.

"We will be legally bound to say we can't guarantee the results and that it's an experiment. We will have to tell them not to take it seriously - that it's entertainment. It's ridiculous."

However, the OFT is determined to enforce the rules in relation to those working in the industry: according to its own research, psychic mailings promising spiritualist services earned £40m between 2006 and 2007.

The scale of rogue trading was revealed earlier this year in research conducted by the UK Government Department for Business, Enterprise and Regulatory Reform, which found that 94% of the people it surveyed had won a competition that they never entered and 80% had experience of a pushy salesman who refused to take no for an answer.

Sarah O'Neill, legal officer with the Scottish Consumer Council, said: "Too often traders have been selling goods and services to customers knowing full well that what they're doing is dishonest.

"It can be special offers' which are not actually in stock, selling goods that are already obsolete or competitions that nobody has a chance of winning.

"What has made it so distasteful has been the fact that victims of misleading and unfair practices are often those most vulnerable in society. This legislation signals a huge step towards putting the perpetrators of scams and mis-selling out of business."

Gareth Thomas, the UK Consumer Affairs Minister, said: "Honest traders understand the value of treating customers fairly and they've had enough of losing profit to the rogues who use underhand tactics to get ahead.

"The consumer protection regulations will deliver better protection for consumers, cut red tape and put in place a simpler and clearer consumer law that will be easier to interpret and enforce."

Andy Millmore, a partner at London law firm Harbottle and Lewis, said: "What is significant is the sweeping nature of the regulations, effectively criminalising actions that might in the past have escaped legal censure.

"What the regulations are designed to do is make sure that any commercial practice that looks unfair and likely to harm consumers in their pockets will be illegal.

"It will, therefore, be picking up the gaps and grey areas that existed under previous UK legislation. For instance, if my aged grandmother lets in a double-glazing seller and he presses to make a sale, preying on the fact that she's too polite to ask him to leave, that would now probably constitute an aggressive practice and be criminalised."