With 5 months to go until our last payment I want to know at what point I can "legally" apply for a vanquish (or similar) credit card to rebuild credit score, and also when I can look at replacing the shed I have made limp along for the last 4 years. I want to borrow about £3k which is well within my budget and will allow me to seek out more work than my current car can be trusted for! I assume both of these will be the day after my final payment has been made?
I don't think it'd be illegal now, although it may break the terms of your IVA, which as far as I know is a civil matter
I'd ask your IP if you could apply for a card and see what they say, they may not be to worried as you have got used to living on a budget and not got left to run
If your IVA does allow credit it's common to limit this to £500, whether your can find anyone to give you such a limit is another matter
Credit is fine provided the IP gives consent and there is nothing illegal about applying for any. However, it could lead to failure of the IVA if you do not ask your IP first but from what you have said I doubt if your IP will have a problem.
There's nothing illegal about it, you just might struggle to be accepted whilst the record of the IVA is still on your file. If you apply before your IVA is completed, you will need to obtain permission from your IP.
Once you have completed all of your obligations under the IVA, you should be able to apply - but you may have more success once your case has been formally closed.