It is true that many tourist guide London jobs do not have formal qualification requirements. You can readily get the job if you have good language and interpersonal skills and a genuine interest in British culture and history. However, if you have formal training you will have a higher chance of securing a better paid job.
You can get formal training and the prestigious Blue Badge qualification from the Institute of Tourist Guiding. The qualifications it offers correspond to National Education levels 2, 3 and 4. Each levels offers training in specific tourist guiding disciplines, methods and skill.
Level 2 focuses on developing your tourist guiding skills to work in a set location or a fixed route, such as a gallery or an open bus tour. If you get level 3 training as well, you will learn how to introduce different sights to tourists. You will also learn how to work in various tourist guiding environments from a single sight to walking around the streets of London. The highest qualification level 4, which gives you Blue Badge qualification, focuses on tourist guiding in all possible environments buses, cars, boats, walking and on site. Training is taken one step further to teach you how to organize and manage guided tours for tourists.
There are no educational requirements for enrolling in such a training course. These training programs are relatively short, with no more than 100 to 200 training hours, depending on the level of qualification you wish to pursue. Upon completing the course, you will have to sit a written exam and pass one or two on site exams. The cost of training varies, but it is around a couple of hundred pounds.
It is a matter of personal choice whether to get formal tourist guide training or not. However, you have to keep in mind that it will certainly boost your chances of getting part time work in London significantly.