finally got my head around this one.
this is what i make of it.
they want £4000 from you for tax. you can either send then £4000 in prommisory notes, ie £10 £20 notes then its deemed paid.
if you send then an I.O.U as payment (which is quite legal) as i see, because its a promise to pay (contract) but there is fuck all they can do with an i.o.u because no one deems it worth anything.
now sending them an i.o.u may be deemed an agreement to pay but the conditions of what that i.o,u says will have an effect, unless you write on the back £4000 paid by way of gift is payment made,
if they dont accept it, and send it back they have refused a valid means of payment and you no longer own them £4000 and they no longer have a right to claim that money,
i.o.u seems to be a valid form of payment, as it equally has no worth like a bank note. it just seems that i need to finalize the fine detail of what the i,o,u should say