I have a Halifax ISA which I want to get rid of as soon as my year's interest has been paid. Does anyone know what exact date this happens on?

It's all down to each ISA's terms and conditions as far as I know, but, unless you have some fixed-term special interest rate or something where withdrawal carries some penalty, then you should be able to close an ISA whenever you like and receive all interest earned up to the point of closure.

By 'get rid of', do you mean just get the cash back in your hand, or are you considering transferring to a different ISA?

I'm going to close it because the interest rate is crap. The maximum allowed will go into a new ISA with National Savings as I want my money where it won't be used to fund lending. NS&I do two ISAs - One that allows you to transfer your whole balance, but has a poorer rate, and one that allows you to pay in the maximum for one year but has a better rate, so I'm going to choose the latter and put the rest into Premium Bonds.

Be aware that if you withdraw money from an ISA (as opposed to arrange a transfer), it will be removed from your tax free ISA allowance for whichever year it applies, and you can't get the 'tax freeness' back.

Generally, if an institution (or specific ISA product) permits transfers in, they tend not to be overly restrictive about how much is transferred in, so it's often the case that you can transfer all of the funds you have in one ISA into another.

If an institution (or specific ISA) doesn't accept transfers, then you can only put in 'new' ISA money from the current year's ISA allowance -- so, up to £3k up to April 5th (depending if you've already used any or all of this year's allowance), and £3600 from April 6th.

I only have £4,100 in there now so I'll close it once the interest has been credited - I guess that'll be on or after 5 April - and put £3,600 of it straight into a new NS&I ISA and the rest, plus a load of other money that I have elsewhere, into Premium Bonds.

My main objectives are as follows:

1: Have nothing in a place where it can be used to support the loans system. As I'm priced-out of the housing market I don't want my savings to be used to write mortgages for people who aren't.
2: Put most of it into Premium Bonds. As rates are pretty poor across the board I'm happy to risk getting no return at all on the off-chance that I might win a decent prize instead.

As I said above, it may not be that there's a specific 'date upon which they pay the interest'. Of course, only you know the details of the ISA product you're referring to, but generally ISAs are just like any other bank account -- interest keeps getting paid (or at the very least calculated) as you go along. On closure, any interest so far not added to the account will be added. For many (perhaps most) ISA, the time of closure is entirely arbitrary -- although, as I think I mentioned, some ISAs do have special terms and conditions, e.g. keep your money in for a year or forfeit 90 days' worth of interest.

In other words, are you sure there's a specific date you're waiting for, or is it some imaginary one?

Isn't it simply one year after you started it?

Do you ever get the feeling you're just talking to yourself?