To celebrate National PI day, a teacher managed an incredible feat of reciting the first 2,500 digits of PI - from memory.

James Harrison, a music teacher at Aldenham School in Elstree, was recorded live on Facebook yesterday going through each and every digit correctly, in the presence of his students and colleagues.

And those students and colleagues were making sure that Mr Harrison was spot too, keeping a close eye on the correct sequence of digits on their papers.

Despite the cameras, Mr Harrison held his nerve to complete the challenge that he had set himself. At the same time, he pushed his ranking from 103 to 73 in the Pi world ranking list.

Pi Day is the annual celebration of the Pi. Pi is the symbol used in mathematics to represent a constant – the ratio of the circumference of a circle to its diameter.

There are infinite digits.

Most of us just know Pi as 3.14 before the struggle sets in.

Speaking about how the challeneg came about, Mr Harrison said: "I first started learning Pi in around 2010 when a friend challenged me to learn the first 50 places. I found this quite easy and just carried on.

"I don't have any set techniques. There seems to be an emotional connection with the numbers - while I'm recalling Pi, there's definitely a faint connection to the place I was when I first looked at them.

"The only time I really practice is every few years around Pi Day when I plan a recital or when I travel long distances to help pass the time. It's great exercise for the brain.

"The ways I practice are typing the numbers into the 'pi trainer' on, writing in a book, imagining, or very close to recital. My wife has heard me do this more than anyone - I'm blessed to have somebody with more patience than me."

Watch Mr Harrison’s remarkable challenge on the Aldenham School Facebook page.