£3000. ISA or ING Interest (4mths)

Walletwatch

Then equally you'd expect them to not accept BACS transfers, but they do.

It's clearly a grey area.

I don't think there is any grey area here. The brochure for the postal ISA and the T&Cs explicitly say that you cannot have branch or internet access to the postal ISA.

Quoting the Abbey website below:

Consider it if...
You want to save up to £3,000 in a tax year without paying any tax on the interest
You want to manage your money completely by post
You want the option to open an account by post or in branch
You want to transfer the proceeds from any existing ISAs you may have
Don't consider it if...
You’ve used your tax free allowance for this tax year
You want to pay more than £3,000 into a maxi stocks and shares ISA in this tax year
You may want to manage your money by phone, Internet, cash machine or Abbey branch

ashcarrot

Also putting in the money into the ISA opens you up to a bigger ISA capacity next year as it will go up to £6000 (based on you having an account this year)

moneyandmountains

The postal ISA can be opened at the branch and Abbey will accept the opening deposit there. However, subsequent deposits have to be via the post, i.e. standard T&Cs.