Apprarently it was down to the Cache Server which was hit the hardest.
"Due to excessive load, a small number of South West Grid for Learning school websites were unavailable for sporadic periods this morning. Our webservers are usually capable of handling hundreds of thousands of visits above the normal levels. With the amount of schools closing and parents repeatedly checking multiple school sites, we were dealing with over a million extra hits per webserver.
Whilst our hardware remained operational, pages were taking a long time to load for some sites which lead some browsers to timeout.
We're now working to increase the effectiveness of these servers for the future. We apologise if parents and teachers struggled to access any if your website resources this morning"