How does HMRC define a lump sum?

The word I got from HMRC was that a "lump sum implies that no further distributions would be made". So they (at least the person who wrote that) appear to be still on the original 100% definition.

This makes me wonder if it would be kosher to open a second IRA, transfer half the funds into it and liquidate one each year? Hmmm.

That is my plan - create new IRA's and move the appropriate amount to each one so each year I am performing a 100% conversion of 'the' IRA to ROTH followed by closing of 'the' IRA making it impossible to repeat.
This process is easy to do and has no US tax consequences
For extra points I will make small trades in each IRA so they are all different too.

I don't see how HMRC would be able to argue that converting all of an IRA to ROTH and closing the account  is NOT a lump sum transaction.