Objective criteria are applied in each case.
TTP arrangements are entered into on a case-by-case basis.
TTP is only agreed where HMRC is satisfied that the customer cannot pay their liability on the actual due date(s).
The customer offers the best payment proposals that they can realistically afford. If their ability to pay improves during the TTP period then they must contact HMRC and increase their payments/clear the debt.
TTP is only agreed where HMRC believes that the customer will have the means to pay the taxes included in the TTP arrangement and any other taxes outside the arrangement which become due during the TTP period.
The TTP period is as short as possible.