JamesS88 has pretty much answered this (thanks!)

You can upgrade before December starts to have the 2TB for December, then downgrade the tariff in the new year - that way you'll have the 2TB for just the two months. (Or downgrade during December and the new tariff will start from January 1st)

What happens to the carry-over from the 2TB if not all used though please Andrew? And am I right in thinking what you say only applies to switching within TTB backhaul? Not if switching from/to BTW where the install cost applies? Though I expect once someone moves to TTB they won't switch back.

If your normal usage is between 200GB and 800GB you can use this to save money!

Month 1 2TB package:
Use 800GB which means you carry over 600GB (half the unused 1.2TB)

Month 2 200GB package:
Starting allowance is 800GB and all is used

Month 3 back to 2TB and keep repeating.

The interesting thing is that it renders the 300GB package totally redundant. Doing as I suggest costs an extra £15 every other month (average £7.50 per month). The 300GB package costs an extra £10 per month!

Sorry - to clarify - the 'Quota Bonus' is 'half of the unused quota from the previous month' - eg:

You're currently on the 2TB tariff...
Duting the month you change to the 200GB tariff (which will start from the start of next month)...
By the end of the month you happen to have 1TB remaining...

The Quota bonus will be 500G.

Andrew, could you confirm my conclusion that anyone using between 201GB and 800GB per month can save money by each month swapping between the 200Gb and 2TB package?

I'd have expected some sort of cap to stop this nonsense, e.g. the maximum quota bonus that can be added to any package at the start of the month is the maximum that can be accrued on the package (e.g. on the 200GB package the maximum bonus is 200GB even if downgrading from 300GB or 2TB).

I had no idea we could swap on a monthly basis - interesting!

In reply to a post by jelv:

If your normal usage is between 200GB and 800GB you can use this to save money!

Month 1 2TB package:
Use 800GB which means you carry over 600GB (half the unused 1.2TB)

Month 2 200GB package:
Starting allowance is 800GB and all is used

Month 3 back to 2TB and keep repeating.

The interesting thing is that it renders the 300GB package totally redundant. Doing as I suggest costs an extra £15 every other month (average £7.50 per month). The 300GB package costs an extra £10 per month!

Your maths work for me. Having moved from an Unlimited package (Zen) to a quota based package (AAISP) with an average monthly consumption of c.175GBs, there must come a point where customers switching packages each month must become a cost driver. That said, I accept that AAISP's flexible package policy and quota rollover does provide a measure of cost-based user constraint. I can happily live with that.

It didn't answer the OP's minimum term questions.

In reply to a post by jelv:

If your normal usage is between 200GB and 800GB you can use this to save money!

Month 1 2TB package:
Use 800GB which means you carry over 600GB (half the unused 1.2TB)

Month 2 200GB package:
Starting allowance is 800GB and all is used

Month 3 back to 2TB and keep repeating.

The interesting thing is that it renders the 300GB package totally redundant. Doing as I suggest costs an extra £15 every other month (average £7.50 per month). The 300GB package costs an extra £10 per month!

You could do that if you wanted

Customer can change their quote tariff whilst in-term - that's OK. either up or down. Contact our sales team for more info...