More than half of the shows currently running in London are offering some sort of a discount from as much as 60% off the face value of the ticket. These discounts are generally offered for performances during the week, however some shows are even reducing the prices on weekends too.
The best place to begin your search would be online. There are many websites offering discount theatre tickets so don't just buy the first tickets you find as you may find similar seats on another website at a cheaper price. Make sure you have a good look around before you hand over your money. Also it is essential that you make sure the company you have chosen to buy tickets from is a full member of STAR. STAR, which stands for the Society of Ticket Agents and Retailers, is the leading self-regulatory body for the entertainment ticketing industry. All agencies who are members of STAR must comply with their code of practice which is designed to help and protect customers.
Always make sure you read the fine print of when a special offer is available. It is very common for someone to see a special offer for example "Chicago tickets now £39.50" and rush straight in and make a booking for a Saturday showing only to realise later that they didn't take notice of the price they were paying and have in fact paid full price. It will always be stated what days and times a special offer is valid so be careful to read the fine print and check the final price before you confirm.
Theatre's will also offer a discount for groups of usually 10 or more people. These rates are also only available during the week but they can take a huge amount off the face value of the ticket. Most ticket agents websites will have all the group discount information on the specific shows page. This is a great idea if you get a group of friends together for a special event like a hens or stags party or even a work Christmas party as a change from the usual restaurant dinner.
Discount theatre tickets are quite easy to come by, especially if you are free to go to a weeknight performance, just remember to make sure you are buying from an authorised dealer and you read the fine print of when discounts are available.