by section 44 on Tue May 04, 2010 2:03 pm
A lot of questions. The answer to many of your questions (1, 4, 5 and, to an extent, 3) depends on exactly what scheme is being used (they are not all the same and consequently the legal analysis is not always the same).
On 2, generally for SDLT purposes HMRC has an enquiry period of 9 months commencing (usually) with the SDLT return filing date. However, if HMRC makes a "discovery" of an underpayment of tax then they can issue an assessment for up to 6 years after the transaction (often referred to as a discovery assessment). Some scheme shops purport to close-off the discovery risk by voluntarily submitting additional information to HMRC with the hope that this would prevent HMRC from later making such a discovery. The effectiveness of such practice is untested with regards TO SDLT. The leading authority (Veltema) on subject of disclosure (in a different context) suggests that a large amount of information and a high technical quality of disclosure is required - even if willing, this may be beyond the capabilities of your average scheme shop and your average professional advisor. For completeness, an assessment can be issued for up to 21 years after the transaction in the case of fraud or negligence.
With regards to 3, if no SDLT has been paid to HMRC and HMRC properly assess that it is due then the SDLT due, interest thereon and any penalties would be due for payment to HMRC irrespective of what was paid in fees to the scheme shop.
If you have so many concerns and questions, I suspect that artifical tax avoidance isn't for you. Potentially, you could legally save money by using a scheme but you risk ultimately paying out far more than you would have otherwise done and you risk uncertainty for a long period of time.