I ran the update with the Storefront Theme still active on Cadac.dfsmarketplace.co.uk and Strahl.dfsmarketplace.co.uk subdomains.
This cause the sites to have the white screen of death for both admin and site. Once I realised what I had done I deleted the storefront theme to release the sites back to default theme and reallocated them to new themes.
When i then reinstalled the Storefront theme all was still good till I reactivated it - when it cause white screen again and needed a second deleting of the Storefront theme to release it back to default.
How can I clear up the debris that will enable me to reinstall Storefront and make it work. Other sites that did not use Storefront have the same problem if I try to activate it.
Let me know a secure way to give you a login and you can go have a look if that helps.