There was a phone number under the name "SPO-Nage Plumbing" posted on the van in the "give Alex a five-word instruction in the most spy-like way" task in Series 9 Episode 9.
When you called the number on the van (the number no longer works), this audio played:
Transcript:
Alex: “Hello, there! You’re through to the Taskmaster…’s assistant, and part-time emergency plumber, Alex Horne. Unfortunately, I am currently either being punished, or in the basement, re-elasticating the Taskmaster’s swimming trunk collection. So I can’t answer your call, hang out, see my family, or have anything to eat. For any queries to do with Taskmaster or SPO’Nage Plumbing Limited, please either call back in two years time or write to your local MP. Also, err this is very important-“