Increasing size of virual box virtual disk

I am running Virtual Box 6.1, both host and clients are Ubuntu 20.04. I have run short of disk space and I want to increase the Virtual disk size.
Having spent a long time looking at different articles and trying different things the one that took me to where I am now is https://www.howtogeek.com/124622/how-to-enlarge-a-virtual-machines-disk-in-virtualbox-or-vmware/

ie Modified the vdi size using the Virtual Media Manager UI
Called VBoxManage modifymedium disk “<path to my vdi>” --resize 36000 # ( I am using virtual box 6.1 so I assume this is the correct call). Rebooted with the GParted Iso added as an optical drive.
However I am unable to increase the partition despite the partition apparently butting up against the newly created unallocated space.

The partition was sitting underneath an extended partition (see sda2) which needs to be increased before the UI will let you increase the partition itself. Doh!