Thanks guya and nun, I understand these points fully.
I guess the cynic in me is reluctant to spend any money on a tax professional as all the evidence points to this being a complete lottery as to what your tax advisor will say. Even IRS agents commonly will state different things depending on which one you talk to and it is not clear at all.
Further, the language used in a 3520 and also even more pertinently the 3520A is very complex and hard to make any clear application to a simple approved pension scheme. This is an added hardship IMHO that the US/UK tax treaty actually speaks to and IMHO is undue. Whether that is defendable or not, I do not know.
So I could spend £100's for a tax advisor to tell me I don't need the 3520. Or I could spend £100's for one to tell me I do. And then £100's more to help me fill it out.... Who is right? I have read opposing information, not just on here (where I cannot verify if someone is lay person or CTA) but on websites of actual CTA firms/individuals! Like I said, it seems a lottery.
Which is why a large part of me seems to think taking the middle ground is perhaps the best option. In other words, I report it on FBAR as a foreign pension of my wife's, and I also fill out 8833 which I personally do not see as simply stating a treaty position but I also see as an information return, as on that form I will state the value at the start of the year, the end of the year, and the contributions made.
My problem and main issue with the 3520 is how I have read a number of stories where filing this can put you into a higher risk category, and if you get this wrong as well you are then higher risk marked and people have also been automatically pursued by a computer in the IRS, with no one to contact about it and no clear appeal without a lawyer, for excessive penalties. Granted this was related to a gift/inheritance part of the form, but it highlights my concern with filing this form, especially when no one can seem to agree with its necessity given the US-UK tax treaty.
J