Could not connect to cran.stat.ucla.edu:80

I am trying to run sudo apt-get update, which I understand to be a prerequisite step to update R with the command sudo apt-get install r-base.

I get as far as this, and then it gets stuck:

Hit:1 http://gb.archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://cran.rstudio.com/bin/linux/ubuntu xenial/ InRelease                        
Hit:3 http://ppa.launchpad.net/marutter/rrutter/ubuntu xenial InRelease                 
Get:4 http://gb.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]             
Hit:5 http://dl.google.com/linux/chrome/deb stable InRelease                            
Get:6 http://gb.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]           
Hit:7 http://gb.archive.ubuntu.com/ubuntu xenial-security InRelease            
Hit:8 https://cran.ma.imperial.ac.uk/bin/linux/ubuntu bionic-cran40/ InRelease 
0% [Connecting to cran.stat.ucla.edu (128.97.86.247)]

After a couple of minutes I get the message Could not connect to cran.stat.ucla.edu:80 (128.97.86.247), connection timed out

My internet connection seems okay.

Based on answers to similar questions, I have tried sudo apt --fix-broken install – this runs very quickly and gives the last line 0 to upgrade, 0 to newly install, 0 to remove and 9 not to upgrade. Based on answers to this question, I have tried changing the download server from the default United Kingdom to the ‘select best server’ recommended http://ubuntu.mirrors.ovh.net/ubuntu, and back again, and I have tried adding -o Acquire::ForceIPv4=true after the apt-get command. Changing the download server changes the list of Hits and Gets, but it still gets stuck connecting to cran.stat.ucla.edu.