Who is the speaker?

(M: ) Hello. I’ m Callum Robertson, and this is London Life. In the program today, let me ask you a question first: What do you think would be the hardest job in Britain? A police officer? Perhaps a deep-sea fisherman? Well, no, according to recent research, being a London taxi driver takes that prize. It’ s really a hard job, really difficult. One reason is the traffic. It’ s getting worse and worse in London. For most of us, if we have to sit in a traffic jam for a few minutes, we get anxious. But imagine if you had to do that all day, every day as your job. What’ s more, passengers get into the taxi and want to get from A to B as quickly as possible. They’ re in a hurry, and that makes things worse for the drivers. To prepare for the test, would-be drivers have to remember ways and places of interest around Central London. This is an area which has about 25,000 streets. They need to be able to take passengers from A to B without having to look at a map and without having to ask for directions. It usually takes nearly three years to pass the test, so it is also found in the research that parts of the brains of taxi drivers are actually larger than those in the general population. It seems as if learning all the streets and ways makes a part of the brain grow. Well, anyway, this is a most tiring job. Next time you’ re stuck in a traffic jam and feel mad, spare a thought for the taxi drivers, who have to spend most of their working life in them.