Actually, I think I've cracked it (with a little help from some friends - see below).
I phoned IRS London at the embassy asked if they could help with the specifics of the 1040 and she said "I can try".
So I asked her about which fields I was actually supposed to fill in under my circumstances. The answers were as follows -
Demographics:
Where the USC is married to a non-USC and you both live outside the US, your filing status should be
Married Filing Seperately. If the spouse has no SSN/ITIN you leave the SSN field for the spouse blank and where it says "enter spouse's full name here" you enter
Non Resident Alien rather than the person's name. Check box 6a, and put the number "1" in
boxes checked on 6a and 6b and in exemptions part 6d
add numbers on lines above.
Onto the bit with the figures:
1040 line 7 is for total worldwide income, but NOT for self-employment income. That's line 12 (for which you attach a schedule C).
Then on 1040 line 21 you list a NEGATIVE amount corresponding to the entire amount of earnings being claimed under the foreign earnings exclusion (as long as it's less than the allowance for 2007, which is $85,700). This is the amount arrived at on form 2555, line 45. This leads to a "total income" of $0, which is listed on 1040 line 22.
Once your official total earnings is zero obviously your tax figure is also zero.
I was told that a form 1116 was not mandatory and only required if you are claiming credit for tax paid in a foreign country. If the full amount earned is less than the maximum foreign income exclusion ($85,700) then this is irrelevant as you don't pay additional tax anyway - so no point in filing it.
Form 2555: I had originally put one or two items in the wrong fields but after I did the online thingamajig at taxact.com and compared my copy to the one it produced - I saw where I went wrong.
Now it all makes more sense. I'm glad I revisited it this morning rather than spending a fortune on a tax professional.
I have one more question on the 2555 form but I can ring IRS London about that (tomorrow - the lines are only open till 12 noon!

). It's relating to item 6a. If you are filing the last 3 years at once, in truth the answer to "have you filed form 2555 before" is actually no - but if one had submitted the forms annually then the answer would be no for 2005, but yes for 2006 and 2007. I will try and clear this up with them tomorrow.
Thanks to all for your input and hopefully the above explanation may also help someone else.