NHS random testing - impossible to log in

My son received a letter from the NHS, inviting him to take part in the random testing for the virus. Fair enough he thought, I'll do my bit to help, and went onto the Internet site address given but it was impossible to find the 'box' to put in the code he was given, as the screen was so disorganised and full of adverts. My son actually works in IT, knows his way around many many IT sites, and is currently an IT help desk advisor. So, if he wasn't able to log in, what hope is there for the less IT literate (me for example....), and for the success of the project?
I've just seen the news with Mat Hancock 'selling' this to the public as supporting the fight against the virus. Ho hum.