Payment on account

[Waldorf]

If you are certain you will have no additional tax to pay for 2015/16 then you can safely reduce your payments on account to zero.

If you get it wrong and do end up owing some tax, you will also owe interest from when they should have been paid on account. There is no fine that I'm aware of (though HMRC would probably take an interest in somebody who routinely abused this facility).

Agreed.

The PoA arises simply because HMRC assumes that your income will be the same in the following year. They have no idea what your income will be which is why, if you know your income will be lower, you can reduce or remove the PoA if you feel it will not be due.

[Contreras]

HMRC should pay 0.5% on the repayment. How much would would the £1800 earn sitting in your account instead?

Is the difference worth waiting in an HMRC call queue, making sense of it, additional filing, worry about penalties?

YMMV, but in many cases people would just suck it up and look forward to the repayment.