Thanks @dan_g I do accept your point. This was not the ideal way of capturing this piece of data, and this will not be normal practice.
Whilst we took every precaution in terms of the choice of service, the content of the email, plus we offered customers the alternative means of contacting us to send the information or verify the email (which several did), this was still something we would have loved to do within the app.
Unfortunately we did not have the relevant field in the app for some of the customers who joined last year, and so we needed to collect this single item as a separate exercise within a specific time-frame.
Even if we had been able to update the app to include it and ask customers to complete it, it would have required all customers to have the very latest version of the app, and this is not always the case. We do encourage everyone to always stay up to date, partly to have these new features, but also to have the very latest fixes and security measures, but it is up to users to update the app.
This is not the kind of exercise we will be doing again, but we are certainly grateful to the huge number of customers who got in touch to provide us with their details. And we are grateful to you for your honest concern and feedback.
On the subject of app updates, there should be a new release in the next week or so with fixes and improvements, so do look out for that.