That’s interesting, and I’m slightly envious, in a funny way.
That said, I’d personally be cautious. I thought the population surveys were being carried out by ONS, not the organisations mentioned. I also thought that one of the weaknesses of ONS Covid-19 studies was, they only ‘used’ people with whom they’d already had contact.
Before responding, it might be worth contacting the relevant organisations via their publicly published phone numbers, to confirm if the approach is genuine.
My hunch is that it is genuine.