The basic common laws of contract formation - offer, acceptance, and so on - apply to sales made over the Internet in the same way as for any other sales.
Sales made over the Internet to individuals are covered by the Consumer Protection (Distance Selling) Regulations (which cover any form of distance selling - for example, sales made over the telephone). These require you to send written confirmation of any order to the customer (by mail or email) containing the necessary information (your name, description of the goods, and so on) and informing the consumer of the right to cancel the order.
If you are selling internationally, it may not be clear where the contract and transaction occur. In some countries, local laws will apply even if your terms and conditions specifically state that the contract is governed by English law. For example, consumers in other European Union countries are protected by their local consumer protection laws, and can take legal action in their local courts.
If you have a presence in a foreign country (eg an office there) transactions may also be subject to local regulation and taxation. You may also run into problems when you do not know who your customer is. For example, selling to minors may be illegal (depending on the country and what you are selling), and contracts with minors are usually unenforceable.
