Solved!

The issue is that HMRC has been crap at explaining things (and Intuit is not much better). Although we are all registered with HMRC and have been filing our returns digitally for years, that does not make us registered for MTD!

To file your VAT return for the final time under the old scheme, in QB, go to file VAT and on the new page, select File VAT (not File VAT MTD). Ignore the warning about “HMRC mandates…” and press Continue. You can then file your VAT in the normal way.

In May, when, and only when, your final payment under the old scheme has been made/taken then log on to the HMRC website and registered for MTD.

Thanks to Jason Oram at Essex Abel Accountants in Loughborough for the insight.

Hope that helps.

Mike