People outside the UK have been banned from attending because they are "agitators". The reason why Palestine Action is illegal is because they organized terrorist attacks, this protest is not illegal and one of the pro-Palestine groups attending is the largest donor to Labour.
Why would foreigners not be allowed to speak? Britain is a diverse melting pot where all peoples can discuss ideas freely. Petty nationalism and xenophobia isn't welcome here.
I didn't mention anything about every immigrant. I am saying that undocumented people have entered the country and carried our terrorist attacks. It isn't impossible to fix this, Labour changed the laws to push people back aggressively in 2004 (iirc, it was before the GE). What has changed is the electoral makeup of the UK, there is a massive constituency for as many illegal immigrants as possible. That is fomenting unrest because it involves massive social and cultural change in order to make up for the fact that Labour's support collapsed amongst their core vote. This isn't a complex or unusual situation: these things are happening because people are heavily incentivised. Changing the law is "wrong"...of course, you wonder why we have't had a working government at the same time? Lol. If any of this stuff was actually fixed, it would be very bad for political parties.