On Monday the #JC4PM tour hit Swansea. The date had been planned months ago and tickets had been selling well before the attempted coup on Jeremy Corbyn. But in the week between the coup and the event, sales went through the roof – and the Brangwyn Hall has a very high ceiling!

People wanted to show support for Corbyn. That was clear from the impromptu rally of a few hundred people that assembled outside the venue just before the show. The was already a buzz about the night before it had started.

Mark Serwotka was a fantastic compere. He not only managed to set the political events of the last two weeks in context, but he was skilled at introducing performers and encouraging audience participation. He was also funny. From the perspective of the audience, it was slick (there is a youtube clip here).

However, backstage, I was in a bit of a pickle. At the weekend I had been informed that John McDonnell couldn’t attend as he now had an important speech to make in London. The way out of all this was to skype John and put it on the projector screen. Easy? We rehearsed it a few hours before the event started and it all seemed straightforward, but at 7pm the wifi signal disappeared.

While I was trying to find new wifi codes for it, I got a phone call. I was tempted not to answer as I was so busy, but I’m pleased I did as it was Jeremy Corbyn. He asked if he could do anything for the night. I was a bit taken aback and said we could try skypeing. He said he would see if this was possible and would call me back.

Then I realised that I was already struggling to get John to skype so I could be wasting a great opportunity if skype fell flat. I texted a message to say that we could do a phone call instead. I then tried to work out how this would work while I was I was also hunting for wifi codes.

The only way possible would be for me to put my phone on speaker and hold it next to the microphone on stage.

Jeremy phoned me back. While Grace Petrie was on stage engaging 800 people in a singalong, I explained that I would be going on stage with the phone. Mark was going to introduce him as I came on.

What happened was incredible. Jeremy was introduced. All that people saw was a phone in my hand, but the idea of the Labour Leader being on the other end generated more noise in the Brangwyn Hall than decades of amped-up Heavy Metal bands. When I actually put the phone to the microphone I realised it wasn’t in speaker mode so I switched it over and then it only took three words from Jeremy to prompt another roar. And then when he finished a few sentences there was more commotion. People started stamping their feet by this time. On a few occasions people didn’t hear what Jeremy was saying as they were making so much noise. It was incredible.

I thought the night was already made but then I had a message saying John had to be skyped within five minutes as soon he had to go and vote in Parliament.

At this point, people were going to get drinks for the interval. I asked the theatre management to get everyone to come back as John was speaking. I then tapped in the wifi code and hooked up my laptop to the projector screen – and John was there! It worked well. People were excited that there was a live transmission and that John was there to explain what was happening in the Labour Party. At one point the picture disappeared, but John’s office called back and the first thing John said was: ‘When we get into power we will make sure we improve Broadband connections’. This got one of the best laughs of the night!

• At short notice a special #Keep Corbyn night has been arranged for the O2 Forum Kentish Town on Tuesday (12 July). The night is compered by Mark Serwotka and features Jeremy Hardy, Francesca Martinez, Michael Rosen, Rufus Hound, Dane Baptiste, Grace Petrie, She Drew The Gun and guest speakers including Jeremy Corbyn. Tickets cost £5/£10/£10 and can be bought online here.