Grandma did Galway Race Course and JPII with her brother and sister-in-law in 1979, no problem. (Bit muddy.)
I saw JPII in Canterbury in 1982, no problem.
I went to Rome in 2000 for WYD where there were 2.1 million people, the city was heaving, like we had to wait 40 minutes underground to get onto the Underground to get back into the city centre after the Papal Mass. No-one pushed, no-one got agitated, people just chatted to each other and then got on a train. There was plenty of water and food and it was all fine. ( A little hot to be fair, but the Fire Brigade sprayed the pilgrims with hoses at regular intervals to keep us cool. It was so hot you could go from soaked to dry in five minutes.)
I've seen people practically charge into Brompton Oratory at the end of the Rosary Rally and it was all fine.
I've been in plenty of packed churches full of candles and never felt worried at all.
So I will be going into London to see the Pope in September and if I don't get a ticket to that Prayer Vigil, I will just have to stand by the side of the road with my flag.
I'm forever getting mixed up into football crowds, Marathon crowds etc on public transport. London is always dealing with hoards of people. Let's not be boring about this.
The thing about Catholicism is you do have to be physically present.
You can't go to confession over the phone.
You can't fulfil your Sunday obligation by watching TV.