UK Tax Questions? Ask a UK Tax Advisor for answers ASAP
Let me take a look at this and I'll get back to you.
If something sounds too good to be true, it probably is. Nobody would have signed up for a scheme such as the Sanzar one unless they were told they would pay significantly less tax. I don't know the nitty gritty of how the schemes worked save to say that participating contractors were paid part of their wages in the form of a a loan, repayable on demand. The "clever" idea was that the "loan" would never be called in or written off, hence the tax saving. HMRC always catch up with these schemes. It's just a matter of time.
As a Sanzar contractor, you should have been offered the chance to take part in the Contractor Loans Settlement Opportunity on favourable terms which you can read about here and here. That opportunity is now gone I'm afraid. You might also read the notes here. As you appear to be in the dark on what you got involved in, you might take a look at the forum here which may provided you with some recommended advisers to represent you in any negotiation with HMRC. Frankly, no matter how good the adviser, HMRC have defeated the Sanzar scheme and you really ought to be looking to settle the case and move on.
I cannot recommend any particular tax investigation firm but there are many involved in this area so it's a matter of googling "Sanzar" and using the forum I gave you a link to to learn about the experience of others and what they are doing. It would appear that many are signing up with WTT BIG Group but I have to say I know nothing about them. Whoever you take advice from on this matter won't be inexpensive.
I'm sorry I cannot offer you any relief from the worry the HMRC demads will be causing but I hope this helps. Let me know if you have any further questions.
I've just clicked on all the links and they all work. I've posted them below. It doesn't surprise me that Sanzar are no longer in existence though the directotrs may have set up under another guise.