Whilst I envy the price windows cleaners can charge in the South of England, we have to be careful with this subject as it can be seen as fitting into the "price fixing, cartels and monopolies" catagory.
Business Link, under the section of Practical Advise for Businesses says:
The law aims to promote healthy competition. It bans anti-competitive agreements to fix prices, makes it illegal to agree not to compete with other businesses, and prevents companies from abusing a dominant market position.
There are heavy penalties for breaking the law. You can be fined, disqualified from being a director - or even sent to prison.
The law also provides extra powers to protect competition. Mergers between businesses can be prevented if they reduce competition. Uncompetitive markets can be investigated and referred to the Competition Commission
Price fixing and the lawCompetition law prohibits almost any attempt to fix prices - for example, you cannot:
agree prices with your competitors, eg you can't agree to work from a shared minimum price list
share markets or limit production to raise prices, eg if two contracts are put out to tender you can't agree that you'll bid for one and let your competitor bid for the other
impose minimum prices on different distributors such as shops
agree with your competitors what purchase price you will offer your suppliers
cut prices below cost in order to force a smaller or weaker competitor out of the market
The law doesn't just cover formal agreements. It also includes other activities with a price-fixing effect. For example, you shouldn't discuss your pricing plans with your competitors. If you then all 'happen' to raise your prices, you are fixing prices.
There are exemptions to the law and some agreements are not prohibited by competition legislation, particularly between companies with insignificant market shares. However, there are very few occasions where an agreement concerning price-fixing would be allowed. To find out more about exemptions, download the Office of Fair Trading (OFT) guide to agreements and concerted practices from the OFT website (PDF, 103K) - Opens in a new window.
Consequences
The law is enforced by the OFT, which can impose a fine of up to 10 per cent of your turnover. It can also apply for company directors to be disqualified.
If you are found to be part of a cartel you could even face criminal prosecution and jail - see the page in this guide on cartels and the law.
http://www.businesslink.gov.uk/bdotg/action/layer?topicId=1074014670Spruce